ArticlePDF Available

Abstract

Iron, the predominant impurity in quartz ores, can be substantially removed via aqueous chemical processes using organic and inorganic acids. Quartz was highly purified by leaching with sulfuric acid (H2SO4) in the presence of reducing agents (oxalic acid, citric acid, and glucose). The effects of the parameters in the leaching tests were evaluated with the full factorial design method and the analysis of variance (ANOVA) method. Higher amounts of ferric oxide (Fe2O3) were removed in the presence of reducing agents during H2SO4 leaching. Under optimum conditions (20% pulp density, 0.5 M H2SO4, 10 g/L of oxalic acid, 90 °C, and 120 min), 98.9% of Fe2O3 was removed, resulting in a final quartz product with 1 ppm of Fe2O3 in the presence of oxalic acid in H2SO4 leaching. Although oxalic acid showed particularly significant effects, citric acid and glucose also produced quartz products with low Fe2O3 content (1.8 and 3.1 ppm of Fe2O3, respectively). The models obtained from the data of H2SO4 leaching with the addition of oxalic acid, citric acid, and glucose, based on the ANOVA results, were suitable for estimating the leaching yield. The process was simulated within the scope of economic modeling studies. These studies showed the economic feasibility of quartz purification by hydrometallurgical processes in obtaining quartz products with high market value and high quality.
Accepted in the IJMP (June 2016)
Iron Removal in Production of Purified Quartz by Hydrometallurgical
Process
Aysenur Tuncuk and Ata Akcil*
Mineral-Metal Recovery and Recycling (MMR&R) Research Group, Mineral Processing Division,
Department of Mining Engineering, Suleyman Demirel University, TR32260 Isparta, Turkey
Abstract
Iron, the predominant impurity in quartz ores, can be substantially removed via aqueous
chemical processes using organic and inorganic acids. Quartz was highly purified by
leaching with sulfuric acid (H2SO4) in the presence of reducing agents (oxalic acid, citric
acid, and glucose). The effects of the parameters in the leaching tests were evaluated with
the full factorial design method and the analysis of variance (ANOVA) method. Higher
amounts of ferric oxide (Fe2O3) were removed in the presence of reducing agents during
H2SO4 leaching. Under optimum conditions (20% pulp density, 0.5 M H2SO4, 10 g/L of
oxalic acid, 90 °C, and 120 min), 98.9% of Fe2O3 was removed, resulting in a final quartz
product with 1 ppm of Fe2O3 in the presence of oxalic acid in H2SO4 leaching. Although
oxalic acid showed particularly significant effects, citric acid and glucose also produced
quartz products with low Fe2O3 content (1.8 and 3.1 ppm of Fe2O3, respectively). The
models obtained from the data of H2SO4 leaching with the addition of oxalic acid, citric
acid, and glucose, based on the ANOVA results, were suitable for estimating the leaching
yield. The process was simulated within the scope of economic modeling studies. These
studies showed the economic feasibility of quartz purification by hydrometallurgical
processes in obtaining quartz products with high market value and high quality.
Keywords: Quartz; Iron Removal; Leaching; Purification; Reducing Agent
__________
* Corresponding author. Tel.: +90-246-2111321.
1/29
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
1
2
E-mail address: ataakcil@sdu.edu.tr (A. Akcil).
1. Introduction
The physical, chemical, and mineralogical characteristics of iron-containing minerals;
appropriate reagents (organic and/or inorganic acid); and optimum conditions must be
determined in leaching procedures (Vegliò et al., 1998; Banza et al., 2006; Tuncuk and Akcil
2014). Vegliò et al. (1998) stated that sulfuric acid (H2SO4) leaching alone is not very
effective in removing iron from a quartz ore, although the addition of oxalic acid increases its
efficiency (35–45% Fe). They reasoned that the high concentration of iron in mica lowered
the efficiency of its removal. Lee et al. (2007) demonstrated that goethite (FeOOH) dissolves
more rapidly and efficiently than ferric oxide (Fe2O3). In a study on the dissolution of some
iron minerals in hydrochloric acid and oxalic acid, iron oxyhydroxides such as FeOOH were
found to dissolve under oxidizing conditions (0.6–0.8 V (Ag/AgCl ref.)), Fe+3 by forming
oxalate complexes, and minerals such as hematite (α-Fe2O3) and maghemite (γ-Fe2O3) only by
reduction (Cepria et al., 2003). These studies demonstrate the significance of the structure of
iron in its removal from quartz.
Nowadays, purified quartz is widely used in several high technology applications; such as
industry of optical fibers, construction of silicon cells for use in photovoltaic systems,
semiconductors for the electronic industry, industrial catalytic chemistry for the synthesis of
catalysts, zeolites and adsorbent materials (Vatalis et al., 2015). When quartz contains less
than 50 µg/g of impurities, which mainly contaminating trace elements (especially Fe and B,
Li, Al, Ge, Ti, Mn, Ca, K, Na, P) in the quartz lattice, quartz is described as purified (Müller
et al.,2007). Generally purified quartz has Fe2O3 <15 ppm, Al2O3<300 ppm and alkali earth
oxides <150 ppm (Richard Flook; Vatalis et al., 2015). In several high technology
applications, silica glass needs to have adequate properties, such as chemical purity, optical
transparency and radiation resistance (Santos et al., 2015). Also impurities especially iron
occurring in these quartz productions is harmful as it impairs transmission in optical fibers
and the transparency of glasses, it discolors ceramic products and lowers the melting point of
refractory materials. (Taxiarchou et al., 1997a)
2/29
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
3
4
Chemical methods include leaching of minerals using organic and inorganic acids (Panias et
al., 1996). The most commonly used inorganic acids are hydrofluoric, hydrochloric, sulfuric,
and perchloric acids. These acids, especially HF, can be extremely hazardous to health and the
environment, and they should eventually be recycled; HF, in particular, causes undesirable
quartz mass losses (Santos et al., 2015). However, the most important advantage of inorganic
acids is their low cost compared with organic acids (Taxiarchou et al., 1997b). However,
products treated with inorganic acids such as H2SO4 and hydrochloric acid (HCl) must be
washed/cleaned thoroughly after the leaching procedure, because it is contaminated with
sulfate (SO4−2) and chloride (Cl) ions. Organic acids are more commonly preferred than
inorganic acids as iron is dissolved more rapidly and efficiently (especially with oxalic acid
and citric acid). They also prevent the precipitation of iron (increasing its solubility) by
forming a complex with the dissolved iron such that leaching can proceed in a wide pH range.
Oxalic, citric, ascorbic, acetic, fumaric, and tartaric acids are used for their ability to dissolve
iron and other metal oxides. Among these organic acids, oxalic, citric, and ascorbic acids are
carboxylic acids, which are used as alternatives to other inorganic acids that are most
commonly used as effective dissolvent reagents and low-cost leaching reagents (Panias et al.,
1996; Ambikadevi and Lalithambika, 2000). In addition, the rate of impurity removal (Fe, Al,
Na, K, Ca, Mg) can be increased partly with the use of complexing agents (citric acid, oxalic
acid, acetic acid, humic acid, ethylenediaminetetraacetic acid (EDTA), and thiourea) (Zhong
et al., 2014)
Among other organic acids, oxalic acid can be used as a leaching reagent to clean industrial
minerals, because of its high efficiency, good complexation property, and good reducing
activity. In addition, oxalic acid can be economically obtained as a by-product from other
industrial procedures. In leaching procedures with added oxalic acid, the dissolved iron waste
can be precipitated from the leaching solution as iron oxalate, which can then be transformed
into pure Fe2O3 by calcination. Similarly, the oxalate that remains in the mineral phase is
removed in the form of carbon dioxide during the thermal procedure (for example, during the
kiln drying stage in ceramic production) (Lee et al., 2006). Oxalic acid was deemed the most
appropriate leaching reagent in a study conducted by Ambikadevi and Lalithambika (2000),
evaluating the performance of different organic acids (acetic, formic, citric, ascorbic, succinic,
3/29
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
5
6
tartaric, and oxalic acids) in removing iron from a kaolin clay sample used as a raw material
for ceramic.
The reaction mechanism of iron oxide dissolution by organic acids was explained in the
following three steps: adsorption of organic ligands in the solution on the surface of the iron
oxide, dissolution, and reducing dissolution during the autocatalytic process. This mechanism
shows that protons participate in the dissolution process (Panias et al., 1996). The temperature
and pH of the solution affect the dissolution of Fe2O3 in acidic oxalate solutions (Taxiarchou
et al., 1997a). The dissolution of Fe2O3 in oxalic acid can be prevented by the formation of a
Fe+2–oxalate product layer at a pH value between 1.6 and 3.2 (Lee et al., 2007; Salmimies et
al., 2012).
Many environmental factors such as pH, organic compounds, and the intensity and
wavelength of the sunlight have been found to influence the dissolution of Fe+3 in aqueous
solution systems and the balance between Fe+2 and Fe+2 (Voelker et al., 1997; Song et al.,
2005). Formate, acetate, citrate, and oxalate (Graedel et al., 1986; Zuo and Holgne, 1992) are
common organic ligands, of which oxalate was found to be most effective ligand in the
dissolution of iron. Fe+3 was observed to dissolve and adsorb onto oxalate ions at a pH of ~2.5
(Xu and Gao, 2008). Many researchers have used oxalic acid in the dissolution of iron oxides
(Segal and Sellers, 1984; Cornell and Schindler, 1987; Jepson, 1988; Panias et al., 1996;
Vegliò et al., 1998; Lee et al., 2007).
Iron oxide is dissolved during leaching with oxalic acid via a photo-electrochemical reduction
process that includes the load transfer mechanism between the dominant types of ferric
oxalate (Fe(C2O4)3−3) and ferrous oxalate, which serves as an autocatalyst (Fe(C2O4)2−2) (Blesa
et al., 1987; Taxiarchou et al., 1997b). The reducing mechanism in this case is a redox
reaction, with oxalate being oxidized to form carbonic acid or carbon dioxide, which occurs in
two half-cells, and Fe2O3 being reduced to form Fe+2–oxalate (Eq. 1). This redox reaction
indicates that hydrogen ions, oxalate, and iron oxide (Fe2O3 particles) are involved in the
leaching procedure. The kinetics of the reaction is determined by the optimum pH (2.5–3.0),
temperature, oxalate concentration and particle size of Fe2O3 (Lee et al., 2006):
4/29
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
7
8
H+ + Fe2O3 + 5HC2O4→ 2Fe(C2O4)2−2 + 3H2O + 2CO2(1)
Carbohydrates such as glucose, sucrose, and lactose are also used as reducing agents in acidic
solutions. Glucose (Trifoni et al., 2001; Ghafarizadeh et al., 2011) was used as a reducing
agent in typical acid leaching procedures to recover manganese from manganese dioxide
(MnO2)-containing ores/wastes. Within the scope of these studies, dissolution of Fe2O3
contained in the ore/waste as Fe+2 into the solution was observed, with possible recovery.
The present study aims to investigate quartz purification by leaching and process simulation
within the scope of economic modeling. Parameters such as reagent concentration,
temperature, pulp density, effect of different reducing agents, and leaching duration were
studied in detail to determine optimum conditions for purifying quartz via the factorial design
method.
2. Experimental
2.1. Experimental Procedure
The quartz ore used in the experiments was provided from Kaltun Madencilik San. ve Tic.
A.Ş. (Cine, Aydın, Turkey). The reserve of quartz ore deposit is more than eight million tons,
and the average Fe2O3 content of the samples used in this study is 310 ppm. The quartz
samples were analyzed using an X-ray fluorescence (XRF, Spectro Xepos) method.
For all experiments, 95–98% H2SO4 solution (Merck) was used as a stock solution and very
pure (>99%) oxalic acid (Merck), citric acid (Merck), and glucose (Merck) were used as
reducing agents. Distilled water was used for the stock solutions and dilutions.
To prepare the quartz sample for the leaching procedure, quartz ore of approximately 5-cm
size was subjected to various size reduction procedures (crushing and grinding), with a final
size of −500 µm. In particular, the Fe2O3 content of the quartz samples of each size was
5/29
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
9
10
analyzed based on sieve fractions after grinding; the subfractions with high Fe2O3 content in
all quartz samples were, in turn, separated using sieves (Retsch) before leaching and enriched
according to particle size.
All leaching tests were performed in 600-mL reactors with glass lids in an analysis volume of
300 mL. The experiment samples were mixed using a magnetic mixer with heater (Velp,
Arec) and a digital overhead mixer (Teflon-coated impeller tip) (Heidolph, RZR 2021) at a
mixing rate of 200 rpm. At the end of the leaching procedure, the filtered and washed samples
were dried at 105 °C in the drying oven for 24 h, and the chemical composition of the samples
was determined with XRF.
The leaching tests were based on 2n full factorial experimental design by considering four
different factors and using the Yates experimental design technique. The factors tested for all
leaching tests and their levels are presented in Table 1. The levels were chosen at specified
rates in order to calculate a wide reflection surface area with analysis of variance (ANOVA)
(Montgomery, 1991). The models were derived from the evaluated data using the multiple
linear regression method with Minitab 14 Statistical Software based on the Yates
experimental design technique.
Table 1
2.2. Economic Modeling
The factorial design for the leaching tests is generally used as a statistical approach to increase
the efficiency of the production process and quality of the product and to determine the effect
of product inputs on the product. Therefore, data from leaching tests were found to be suitable
for use in economic modeling studies. For this purpose, SuperPro Designer Version 2.71
Software, which was developed by Intelligen Inc., was used. The facility was simulated with
the software; the units required for the facility, the operating conditions of these units, the
reactions realized in the units, and the required chemicals were determined and entered in the
system; and the facility flow diagram, costs, expenditures, the amount of product obtained,
and its economic value were stated.
6/29
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
11
12
3. Results and Discussion
3.1. Quartz characterization and preliminary processes
Studied quartz ore sample is mainly composed of 99.21% silicon dioxide (SiO2), 0.39%
aluminum oxide (Al2O3), 0.031% Fe2O3, 0.014% titanium dioxide (TiO2), 0.06% calcium
oxide (CaO), 0.07% sodium oxide (Na2O), 0.07% magnesium oxide (MgO), and 0.02%
potassium oxide (K2O).
Macroscopic and microscopic analyses revealed the presence of hematite, in the form of
Fe2O3. Hematite was found in quartz sample as plastering and filling in the cracks of the
quartz. Therefore, the sample was enriched to the particle size and the subfractions were
separated starting from −106 μm (Table 2). The Fe2O3 and titanium oxide (TiO2) contents
were reduced to 88 ppm and 71 ppm, respectively, in the quartz sample. The sample between
−500 and +106 µm was used in leaching tests.
Table 2
3.2. Factorial design leaching tests and ANOVA
Leaching tests that included all possible combinations of each factor level were performed
with the factorial design. The factors used in high and low levels are denoted by (+) and (−),
respectively, and the midpoint (midlevel) of the experiment was denoted by (0) (Table 3).
Because many variable parameters had to be controlled, the experimental results were
statistically analyzed using ANOVA for examining the effect of significant parameters only
instead of all parameters.
Table 3
As shown in Table 3, Fe2O3 was removed at the end of the H2SO4 leaching procedures by
adding oxalic acid, citric acid, and glucose under experimental conditions based on the full
factorial design. The effective values of the main and interaction factors affecting the removal
of Fe2O3 during the leaching experiments are presented in Figs. 1–3.
Fig. 1
7/29
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
13
14
In Fig. 1, the main and interaction factors were selected using the Yates design method. The
main effects of pulp density (A) and H2SO4 concentration (B) on Fe2O3 removal were found to
be insignificant. The main effects of oxalic acid concentration (C) and temperature (D) on
Fe2O3 removal were positive. Fe+3 is reduced to Fe+2 and Fe2O3 is dissolved in the presence of
oxalic acid as a reducing agent, which was observed to have a significantly positive effect on
Fe2O3 removal. High amounts of Fe2O3 were removed at all tested oxalic acid concentrations.
However, the interaction effect of H2SO4 concentration with oxalic acid was observed to be
negative. As stated in previous studies, this situation is explained as follows: although the iron
leaching efficiency tends to increase with acid concentration, it decreases if the acid
concentration exceeds a certain value in the oxalic acid medium (Vegliò et al., 1998; Lee et al,
2007). The most important interaction effects on Fe2O3 removal were observed to be CD
(positive), AB (positive), and ABCD (negative). The interaction effect of oxalic acid with
temperature (CD) was also observed to be high and positive. While their main effects were
not observed, the interaction effect of pulp density (A) with H 2SO4 concentration (B) was
observed to be positive. High pulp density and high H2SO4 concentration have a significant
effect on Fe2O3 removal.
According to the data of H2SO4 leaching with the addition of oxalic acid, the ACD, BCD, and
ABCD tests removed the highest amounts of Fe2O3 of 98.9% (Table 3, Test no. 14, 15, and
16). At the end of H2SO4 leaching with added oxalic acid under optimum conditions based on
the Fe2O3 removal values, the whiteness index of the quartz product was found out to be 90.6.
These results showed that oxalic acid can be used as a reducing agent to efficiently increase
the leaching yield.
At the end of a leaching period of 120 min, 98% of Fe2O3 was removed by H2SO4 leaching
with citric acid added at a rate of 5 g/L under experimental conditions of 10% pulp density,
0.5 M H2SO4 concentration, and 90 °C (Test no. 9). As a reducing agent, citric acid increased
the rate of Fe2O3 removal. These results show that citric acid can also be used effectively in
place of oxalic acid. At the end of H2SO4 leaching with citric acid being added under optimum
conditions according to the Fe2O3 removal values, the whiteness index of the quartz product
was found to be 87.8.
8/29
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
15
16
The results obtained from the H2SO4 leaching experiments with citric acid instead of oxalic
acid as a reducing agent showed the effective main effects of pulp density (A) and
temperature (D) on Fe2O3 removal. High amounts of Fe2O3 were removed especially at high
temperatures. Although the main effect of citric acid concentration (C) was not significant, the
combined interaction effect of H2SO4 concentration with citric acid concentration (BC) was
positive. As the interaction effect of H2SO4 concentration with citric acid concentration (BC)
was positive on reducing Fe+3 to Fe+2, H2SO4 concentration is considered to be more effective
when used with citric acid in leaching tests. High amounts of Fe2O3 were removed when high
citric acid and H2SO4 concentrations were used together (Fig. 2).
Fig. 2
In the H2SO4 leaching experiments with glucose added at a rate of 5 g/L, 96.5% of Fe2O3 was
removed under conditions of 20% pulp density, 1 M H2SO4 concentration, and 90 °C at the
end of a leaching period of 120 min (Test no. 10). High amounts of Fe2O3 were removed
using glucose as a reducing agent. Similar to oxalic and citric acid, glucose can also be used
as an efficient reducing agent in H2SO4 leaching. At the end of H2SO4 leaching with glucose
under optimum conditions according to the Fe2O3 removal values, the whiteness index of the
quartz product was found to be 90.9.
In H2SO4 leaching experiments with glucose as a reducing agent, the main effect of H2SO4
concentration (B) and glucose concentration (C) on Fe2O3 removal was observed to be <%5.
The temperature (D) main factor was also not a significantly effective parameter in H2SO4
leaching experiments with the glucose; high yields were obtained in the facility even at low
temperatures. The interaction effects of pulp density with glucose concentration (AC), H2SO4
concentration with temperature (BD), and glucose concentration with temperature (CD) Fe2O3
removal was negative (Fig. 3).
Fig. 3
The following equations were obtained using Minitab 14 Statistical Software for Fe2O3
removal with H2SO4 leaching with the addition of oxalic acid, citric acid and glucose (Eqs. 2–
4):
9/29
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
17
18
YFe2O3 = 78.394 + 3.831X3 + 6.031X4 + 4.144X1X2 + 1.046X1X3 - 2.244X2X3 +
2.906X2X4 + 9.319X3X4 - 5.031X1X2X3X4 (R2:0.89) (2)
YFe2O3 = 82.244 - 1.931X1 + 6.869X4 + 2.231X1X2 - 1.456X1X4 + 1.731X2X3 + 1.531X2X4
+ 2.081X1X2X4 - 3.444X2X3X4 (R2:0.91) (3)
YFe2O3 = 79.944 + 4.281X1 - 2.181X2 - 0.819X3 - 5.031X1X3 - 0.869X1X4 + 0.681X2X3 -
4.956X2X4 - 4.294X3X4 - 1.656X1X2X3 + 5.406X1X2X4 + 2.181X2X3X4 (R2:0.95) (4)
A linear relationship was found between the results of the experiments and efficient
parameters (>95% significance), and a model based on the efficient values was created. The
Fe2O3 removal efficiency of this model was calculated using Minitab 14 Statistical Software.
The regression equities and coefficients (R2) were assessed to test the convenience of the
model. The distribution of the relationship between experimental Fe2O3 removals and Fe2O3
removals calculated from regression models is shown in Fig. 4. The distributions observed
between the experimental and calculated Fe2O3 removals were good. The distribution graphs
show that the models are consistent with the experimental results, and they can be
successfully implemented in H2SO4 leaching experiments with oxalic acid, citric acid, and
glucose as reducing agents.
Fig. 4
The highest Fe2O3 removal was 86.6%, and 11.8 ppm Fe2O3 content quartz product with a
whiteness index value of 90.6 was obtained with the same quartz sample, after 120 min of
treatment at 90°C with a 10% S/L ratio and 1M H2SO4 (Tuncuk and Akcil, 2014). Besides, in
this study, addition of the reducing agents (oxalic acid, citric acid, and glucose) increased the
leaching yields of Fe2O3 removal.
10/29
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
19
20
The maximum amounts of Fe2O3 removed and the whiteness index values obtained from the
leaching tests are given in Fig. 5. The optimum conditions for H2SO4 leaching with oxalic
acid were 20% pulp density, 0.5 M H2SO4, 10 g/L of oxalic acid, 90 °C, and 120 min; H2SO4
leaching with citric acid 10% pulp density, 0.5 M H2SO4, 5 g/L of citric acid, 90 °C, and 120
min; and H2SO4 leaching with glucose 20% pulp density, 1 M H2SO4, 5 g/L of glucose, 90 °C,
and 120 min. In accordance with the experimental results and the ANOVA evaluations, the
leaching method can be used as a hydrometallurgical process to obtain purified quartz
products with high market value and high quality.
Fig. 5
3.3. Process Evaluation
The process most appropriate for the facility was selected according to the results obtained
from leaching experiments, and a facility operation simulation was created. Technical and
economic analyses were conducted using flowcharts of the facility and market conditions.
The selected quartz purification procedures were performed in the following four phases:
crushing, grinding, enriching according to particle size, and leaching. A flowchart of the
process was created, and the facility was designed as a batch facility.
In H2SO4 leaching with oxalic acid, the following chemical reactions occurred during the
acidic leaching stage with the respective mass balances (Eqs. 5–6):
Fe2O3 + 2H2SO4 + H2C2O4 → 2FeSO4 + 3H2O + 2CO2 (5)
159.7g Fe2O3 + 196g H2SO4 + 90g H2C2O4 → 303.7g FeSO4 + 54g H2O + 88g CO2(6)
11/29
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
21
22
The quartz ore was first preprocessed with crushing, grinding, and sieving (enrichment
according to the particle size). The preprocessed quartz sample was then subjected to
leaching. Various acids enable the dissolution of Fe2O3 in the leaching stage. The purified
quartz left on the filter is considered as the final product, the iron that passes into the solution
can be recovered after precipitation using calcium hydroxide (Ca(OH)2) or sodium hydroxide
(NaOH). The quartz purification process was simulated using SuperPro Designer Program, as
shown in Fig. 6. The specifications of the reactor designed for the leaching process are
presented in Table 4.
Fig. 6
Table 4
A summary chart of the economic process analysis of the simulated quartz product was
obtained. Based on the economic analysis, the project started construction in 2014, lasting for
24 months. The life of the project was considered to be 10 years, and the inflation rate was
chosen as 5%. Designed for simulation with a predicted life, the quartz purification facilities
will pay for its investment cost in approximately 3 years. The facility can earn $32.57 in a
year for each $100 invested. The data collected on the sales values of the quartz product and
the summary chart of the economic process analysis are shown in Table 5.
Table 5
4. Conclusions
Higher Fe2O3 removal is observed when reducing agents in H2SO4 leaching tests. In
particular, 98.9% of Fe2O3 was removed to obtain a quartz product with 1 ppm of Fe2O3 with
the addition of oxalic acid in the H2SO4 leaching tests. Fe2O3 contents of 1.8 and 3.1 ppm
were obtained in the H2SO4 leaching tests with citric acid and glucose, respectively. The
models obtained from the data of H2SO4 leaching with the addition of oxalic acid, citric acid,
and glucose, based on the ANOVA results, were found to be suitable for estimating the
leaching yield. Reducing agents can be used in full-scale procedures to increase the efficiency
of H2SO4 leaching. According to the ANOVA results, the temperature (D) as main factor was
positively effective when oxalic acid and citric acid were used as reducing agents, and H2SO4
concentration (B) showed no significant effect on the leaching yield. Because of the positive
effect of oxalic acid concentration (C) in leaching tests, the environmentally harmful effects
12/29
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
23
24
of H2SO4 during the process applications can be reduced and the use of organic acids can be
extended; and thus environment-friendly process is recommended.
The SuperPro Designer simulation software was used to assess the economic feasibility of the
quartz purification procedure in full-scale practices. In the simulation, H2SO4 was used at the
acidic leaching stage and oxalic acid as a reducing agent in the quartz purification process as
they are more economical than the other chemicals, while also being effective in removing
Fe2O3. By using an organic acid such as oxalic acid, the amount of H2SO4 used in the facility
was reduced and an environment-friendly process with higher efficiency was designed.
Overall, the results show that purified quartz was produced removing major impurities (98.9%
of Fe2O3 removed) via the leaching method. The experimental results suggest that the clean
quartz can be marketed and used as a raw material in the optical quartz industry.
Acknowledgments
This research was supported by research grants from the Research Projects Coordination Unit
of the Suleyman Demirel University (project numbers BAP 1804-D-09 and BAP 2508-M-10).
The authors would like to thank Kaltun Madencilik San. ve Tic. A.S. (Aydin, Turkey) for
kindly providing the quartz ore.
References
Ambikadevi, V.R., Lalithambika, M., 2000. Effect of Organic Acids on Ferric Iron Removal
from Iron-stained Kaolinite. Applied Clay Science, 16, 133-145.
Banza, A.N., Quindt, J., Gock, E., 2006. Improvement of the Quartz Sand Processing at
Hohenbocka. International Journal of Mineral Processing, 79, 76-82.
Blesa, M.A., Marinovich, H.A., Baumgartner, E.C., Maroto, A.J.G., 1987. Mechanism of
Dissolution of Magnetite by Oxalic Acid-Ferrous Ion Solutions. Inorganic Chemistry, 26
(22), 3713-3717.
13/29
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
25
26
Cepriá, G., Usón, A., Pérez-Arantegui, J., Castillo, J. R., 2003. Identification of Iron(III)
Oxides and Hydroxy-oxides by Voltammetry of Immobilised Microparticles. Analytica
Chimica Acta, 477, 157-168.
Cornell, R.M., Schindler, P.W., 1987. Photochemical Dissolution of Goethite in Acid/Oxalate
Solutions. Clays and Clay Minerals, 35 (5), 347-352.
Ghafarizadeh, B., Rashchi, F., Vahidi, E., 2011. Recovery of Manganese from Eectric Arc
Furnace Dust of Ferromanganese Production Units by Reductive Leaching. Minerals
Engineering, 24, 174-176.
Graedel, T.E., Mandich, M.L., Weschler, C.J.J., 1986. Kinetic Model Studies of Atmospheric
Droplet Chemistry. Homogeneous Transition Metal Chemistry in Raindrop. Journal of
Geophysical Research, 91, 5205-5221.
Jepson, W.B., 1988. Structural Iron in Kaolinites and in Associated Ancillary Minerals. In:
Stucki, J.W., Goodman, B.A., Schwertmann, U. (Eds.), Iron in Soils and Clay Minerals.
NATO ASI Ser, 217. D. Reidel Publ. Co., Dordrecht, 467–536.
Lee, S.O., Tran, T., Park, Y.Y., Kim, S.J., Kim, M.J., 2006. Study on the Kinetics of Iron
Oxide Leaching by Oxalic Acid. International Journal of Mineral Processing, 80, 144-152.
Lee, S.O., Tran, T., Jung B.H., Kim, S.J., Kim, M.J., 2007. Dissolution of Iron Oxide Using
Oxalic Acid. Hydrometallurgy, 87, 91-99.
Montgomery, D.C., 1991. Design and Analysis of Experiments. John Wiley & Sons, 649p,
NewYork.
Müller, A., Ihlen, P.M., Wanvik, J.E., Flem, B., 2007. High purity quartz mineralisation in
kyanitequartzites. Norway, Miner Deposita, 42, 523.
Panias, D., Taxiarchou, M., Douni, I., Paspaliaris, I., Kontopoulos, A., 1996. Thermodynamic
Analysis of the Reactions of Iron Oxides: Dissolution in Oxalic Acid. Canadian
Metallurgical Quarterly, 35, 363-373.
Salmimies, R., Mannila, M., Kallas, J., Häkkinen, A., 2012. Acidic Dissolution of Hematite:
Kinetic and Thermodynamic Investigations with Oxalic Acid. International Journal of
Mineral Processing, 10 (111), 121-125.
14/29
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
27
28
Santos, M.F.M., Fujiwara, E., Schenkel, E.A., Enzweiler, J., Suzuki, C.K., 2015. Processing
of Quartz Lumps Rejected by Silicon Industry to Obtain a Raw Material for Silica Glass.
International Journal of Mineral Processing, 135, 65-70.
Segal, M.G., Sellers, R.M., 1984. Redox Reactions at Solid-Liquid Interfaces. In Sykes, A.G.
(Ed.), Advances in Inorganic and Bioinorganic Mechanisms (97-129). Academic Press,
384p, London.
Song, G., Cao, C-N., Chen, S-H., 2005. A Study on Transition of Iron from Active into
Passive State. Corrosion Science, 47 (2), 323-339.
Taxiarchou, M., Panias, D., Douni, I., Paspaliaris, I., Kontopoulos, A., 1997a. Removal of
Iron from Silica Sand by Leaching with Oxalic Acid. Hydrometallurgy, 46, 215-227.
Taxiarchou, M., Panias, D., Douni, I., Paspaliaris, I., Kontopoulos, A., 1997b. Dissolution of
Hematite in Acidic Oxalate Solutions. Hydrometallurgy, 44, 287-299.
Trifoni, M., Toro, L., Vegliò, F., 2001. Reductive Leaching of Manganiferous Ores by
Glucose and H2SO4: Effect of Alcohols. Hydrometallurgy, 59 (1), 1-14.
Tuncuk, A., Akcil, A., 2014. Removal of iron from quartz ore using different acids: a
laboratory-scale reactor test study using a complete factorial design. Mineral Processing
and Extractive Metallurgy Review, 35 (4), 217-228.
Vatalis, K.I., Charalambides, G., Benetis, N.P., 2015. Market of high purity quartz innovative
applications. Procedia Economics and Finance, 24, 734-742.
Vegliò, F., Passariello, B., Barbaro, M., Plescia, P., Marabini, A.M., 1998. Drum Leaching
Tests in Iron Removal from Quartz Using Oxalic and Sulphuric Acids. International
Journal of Mineral Processing, 54, 183-200.
Voelker, B.M., Morel, F.M.M., Sulzberger, B., 1997. Iron Redox Cycling in Surface Waters:
Effect of Humic Substances and Light. Environmental Science Technology, 31, 1004-
1011.
Xu, N., Gao, Y., 2008. Characterization of Hematite Dissolution Affected by Oxalate
Coating, Kinetics and pH. Applied Geochemistry, 23, 783-793.
15/29
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
29
30
Zhong, L., Lei, S., Wang, E., Pei, Z., Li, L., Yang, Y., 2013. Research on Removal Impurities
from Vein Quartz Sand with Complexing Agents. Applied Mechanics and Materials, 454,
194-199.
Zuo, Y., Holgne, J., 1992. Formation of Hydrogen Peroxide and Depletion of Oxalic Acid in
Atmospheric Water by Photolysis of Iron(III)-oxalato Complexes. Environmental Science
Technology, 26, 1014-1022.
16/29
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
31
32
Table Captions
Table 1. Factors and levels investigated in leaching tests
Table 2. Details of the chemical analyses of the quartz samples after beneficiating according
to particle size
Table 3. 24 full factorial design experimental conditions in sulfuric acid leaching in the
presence of oxalic acid,a citric acid,b glucose,c and Fe2O3 removal yields
Table 4. Characteristics of reactor designed for the leaching stage
Table 5. Details of the economic process analysis of the quartz product
17/29
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
33
34
Figure Captions
Fig.1 Main and interaction effects of the studied factors on Fe2O3 removal, according to the
sulfuric acid leaching tests in the presence of oxalic acid
Fig.2 Main and interaction effects of the studied factors on Fe2O3 removal, according to the
sulfuric acid leaching tests in the presence of citric acid
Fig.3 Main and interaction effects of the studied factors on Fe2O3 removal, according to the
sulfuric acid leaching tests in the presence of glucose
Fig. 4 Scatter diagram of the experimental Fe2O3 removal versus that calculated from sulfuric
acid leaching test in the presence of oxalic acid (A), citric acid (B) and glucose (C)
Fig. 5 The highest amounts of Fe2O3 removed and whiteness index values obtained from
optimum leaching conditions (OA: oxalic acid, CA: citric acid, GL: glucose)
Fig. 6 Purified quartz product flow diagram created with SuperPro Designer Software
18/29
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
35
36
Table 1. Factors and levels investigated in leaching tests
H2SO4 leaching in the presence of oxalic acid
Code Factors
Level
Low
(−1)
High
(1)
A Pulp density (%) 10 20
B H2SO4 concentration (M) 0.5 2.0
C Oxalic acid concentration (g/L) 2 10
D Temperature (°C) 70 90
H2SO4 leaching in the presence of citric acid
Code Factors
Level
Low
(−1)
High
(1)
A Pulp density (%) 10 20
B H2SO4 concentration (M) 0.5 1.0
C Citric acid concentration (g/L) 5 15
D Temperature (°C) 70 90
H2SO4 leaching in the presence of glucose
Code Factors
Level
Low
(−1)
High
(1)
A Pulp density (%) 10 20
B H2SO4 concentration (M) 1 2
C Glucose concentration (g/L) 5 20
D Temperature (°C) 70 90
Leaching duration: 120 min
19/29
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
37
38
Table 2. Details of the chemical analyses of the quartz samples after beneficiating according to
particle size
Compound 500 + 106 µm
%
−106 µm
%
SiO299.60 97.91
Al2O30.0553 1.05
Fe2O30.0088 0.0595
TiO20.0071 0.0675
CaO 0.017 0.16
MgO 0.034 0.183
Na2O 0.14 0.35
K2O 0.015 0.075
L.O.I.a0.15 0.15
aLoss of ignition
20/29
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
39
40
Table 3. 24 full factorial design experimental conditions in sulfuric acid leaching in the presence of oxalic acid,a citric acid,b glucose,c and Fe2O3
removal yields
Test
No. Treatment A
(pulp density)
B
(H2SO4)
C
(reducing agent)
D
(temperature)
Fe2O3 removala
(%)
Fe2O3 removalb
(%)
Fe2O3 removalc
(%)
1 (1) - - - - 79.7 80.1 59.0
2 a + - - - 76.0 81.4 85.0
3 b - + - - 80.6 68.9 73.9
4 ab + + - - 75.1 70.3 87.2
5 c - - + - 76.0 72.7 74.9
6 ac + - + - 66.1 68.9 89.0
7 bc - + + - 53.1 81.7 90.6
8 abc + + + - 72.3 79.0 78.4
9 d - - - + 75.9 98.0 94.0
10 ad + - - + 54.4 75.1 96.5
11 bd - + - + 66.0 94.0 58.9
12 abd + + - + 88.8 96.6 91.6
13 cd - - + + 93.6 90.3 85.6
14 acd + - + + 98.9 82.4 73.0
15 bcd - + + + 98.9 87.7 68.4
16 abcd + + + + 98.9 88.8 73.1
17 I 0 0 0 0 87.7 84.4 86.0
18 II 0 0 0 0 88.1 82.2 86.5
19 III 0 0 0 0 90.8 81.0 85.1
21/29
576
577
578
41
42
Table 4. Characteristics of reactor designed for the leaching stage
Characteristics Process
Liquid/Total volume 0.80
Height/Diameter 2.50
Agitation rate 0.50 kW/m3
Vessel temperature 90 °C
Residence time 3 h
Maximum volume 50 m3
Operating pressure 1.01 bar
Height 3.00 m
Diameter 1.20 m
Total volume 3.38 m3
Power 1.4 kW
Heating 80,296.2 kcal/h
Cooling 0 kcal/h
22/29
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
43
44
Table 5. Details of the economic process analysis of the quartz product
Total investment (in thousand $) Process
Purchase cost 125
Direct cost 362
Indirect cost 218
Total plant cost (TPC) 580
Direct fixed capital cost (DFC) 667
Working capital 43
Startup cost 33
Total investment 743
Annual operating cost (in thousand $/year)
Fixed 96
Variable 1491
Depreciation 106
Total annual operating cost 1693
Project indicators
Life time 10 years
Investment payback percentage 32.57
Payback time 3.07 years
Total revenues (thousand $/year) 1965
Unit production costs 1.72 US$/kg
23/29
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
45
46
Fig. 1
24/29
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
47
48
Fig. 2
25/29
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
49
50
Fig. 3
26/29
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
51
52
Fig. 4
27/29
689
690
691
692
693
694
695
696
697
53
54
Fig. 5
28/29
698
699
700
701
55
56
 


 !
"#$%&'()
*+,
-..
/
0
12
13#4#5677897
!:%
;;#<2#=< >
?17#@
A1BC
DEF#G1H#=<
IG>
JKL
M+#
#N(
O#P K#6Q567
&#R
SQ#TU#597
Fig. 6
29/29
702
703
57
58
... Quartz sand with SiO 2 grade between 96 and 99% and Fe 2 O 3 content less than 0.5% is used in industries such as glass, ceramics, casting sand, cement products, chemical industry, filtration, plastic, and abrasive applications. High-purity quartz sand (SiO 2 grade at least 99.90%) is non-metallic high-tech raw material, which is mainly used in microelectronics, fiber optics, electromagnetic materials, refractories, bioengineering, solar cells, aerospace industry, military industry, high-quality ceramic production, and silicon production for photovoltaic applications [2][3][4][5][6][7][8]. ...
... Generally, high-purified quartz has Fe 2 O 3 < 15 ppm, Al 2 O 3 < 300 ppm, and alkali earth oxides < 150 ppm. In addition, silica glass should have properties such as chemical purity, optical transparency, and radiation resistance [5,[13][14][15]. In order to obtain high-purity quartz, it is necessary to reduce the iron content, which is the main contaminant, to the desired level. ...
Article
Full-text available
This study aimed to remove the contaminants in quartz sand by using an eco-friendly method and to obtain high-purity quartz. For this purpose, ultrasound-assisted acid leaching was applied. Equal amounts of a mixture of diluted hydrochloric and oxalic acids were used as the solvent. Response surface methodology (RSM) was used for optimizing, modeling, and predicting the experimental parameters. The correlation coefficient (R2) of the proposed quadratic model for the relationship between iron removal yield and test parameters was calculated as 0.9731 and it was determined that the predicted and actual values were compatible. Finally, optimization experiments were made and optimum experiment conditions were revised and determined as 83.38 °C of leaching temperature, 196.35 min of leaching time, 2.86 M of acid concentration, and 202.24 W of ultrasound power. Under the optimum conditions determined after optimization, the highest yield of iron removal was determined as 95.08%. Under the optimal parameters, the SiO2 content of the concentrates increased from 97.841 to 99.907% and the Fe2O3 content reduced from 0.225 to 0.011%.
... Especially HF, are very dangerous to human health and the environment, and must be recycled. On the other hand, the clay products must be required washing after the leaching, since hydrochloric and sulfuric acids can easily contaminate the product with SO4 2and Cl - (Santos et al., 2015;Tuncuk and Akcil, 2016). Organic acids (oxalic, citric, ascorbic, gluconic, malic acid) are often preferred because of their advantages such as higher iron removal yield, ability to proceed in a wide pH ranges as they prevent iron precipitation and being a more eco-friendly product compared to inorganic acids (Panias et al., 1996;Mandal and Banerjee, 2004;Lee et al., 2006;Lori et al., 2007;Zhong et al., 2013;Tuncuk and Akcil, 2016;Lima et al., 2017;Vapur et al., 2017;Garg and Skibsted, 2019;Pariyan et al., 2019). ...
... On the other hand, the clay products must be required washing after the leaching, since hydrochloric and sulfuric acids can easily contaminate the product with SO4 2and Cl - (Santos et al., 2015;Tuncuk and Akcil, 2016). Organic acids (oxalic, citric, ascorbic, gluconic, malic acid) are often preferred because of their advantages such as higher iron removal yield, ability to proceed in a wide pH ranges as they prevent iron precipitation and being a more eco-friendly product compared to inorganic acids (Panias et al., 1996;Mandal and Banerjee, 2004;Lee et al., 2006;Lori et al., 2007;Zhong et al., 2013;Tuncuk and Akcil, 2016;Lima et al., 2017;Vapur et al., 2017;Garg and Skibsted, 2019;Pariyan et al., 2019). Especially, oxalic acid has been reported to be more effective for iron removal and brightness improvement (Ambikadevi and Lalithambika, 2000). ...
Article
Full-text available
Clay is widely used in a number of industries due to its special properties like fine particle size, brightness and whiteness, chemical inertness, platy structure, etc. In this study, the general characteristics of clays have been investigated by XRF, XRD, FT-IR, TG-DTA and SEM. The presence of iron as an impurity decreases its commercial value due to giving unwanted colors to clay mineral. Therefore, the dissolution capacity of clay ore was investigated by oxalic acid leaching. Under optimized leaching conditions (0.8 M oxalic acid concentration, 85°C reaction temperature, 1.75 ambient pH,-106+75 µm particle size, 15% w/v solids concentration and 150 min. leaching time) with 250 rpm stirring, 83.90% of Fe2O3 was removed. The amount of iron oxide, the main impurity in the clay, has been reduced from 2.70 to 0.40%. The iron dissolution kinetics was mainly controlled by internal diffusion control of shrinking core model and activation energy, Ea, of 26.29 kJ/mol was obtained for the process. The results also showed that the studied clays have adequate characteristics for ceramics industry, earthenware and porcelain production.
... During this process, the iron oxides, as impurity metals, are removed by acids. [1][2][3][4][5] Inorganic (HCl and HNO 3 ) and organic acids (oxalic, acetic, L-ascorbic, and citric acids) have been studied for the iron oxide dissolution. [1][2][3][4][5][6][7][8] Among them, oxalic acid has been suggested to be the most promising acid due to its high acid strength, complexing ability, and reducing property. ...
... [1][2][3][4][5] Inorganic (HCl and HNO 3 ) and organic acids (oxalic, acetic, L-ascorbic, and citric acids) have been studied for the iron oxide dissolution. [1][2][3][4][5][6][7][8] Among them, oxalic acid has been suggested to be the most promising acid due to its high acid strength, complexing ability, and reducing property. [8][9][10][11][12] Moreover, since it can be easily decomposed by calcination, there is no risk of contaminating the treated materials. ...
Article
Full-text available
Oxalic acid has been identified as a sustainable chemical enabling an efficient recovery of target metals from industrial minerals by dissolution. The dissolution process recently has attracted attention as a key reaction in a potential clean iron-making. In this application to efficiently produce a high-purity iron, the dissolution is required to occur in the absence of light, with no addition of other chemical reagents, and to produce high concentration iron oxalate aqueous solution as fast as possible. To reveal the chemistry of iron oxide dissolution for this application, in the present study, the dissolution experiments are carried out under various conditions with a particular focus on the iron oxide highly loaded in the oxalic acid aqueous solution. Highly acidic oxalic acid solution for dissolving the highly loaded iron oxide enabled the production of iron oxalates aqueous solution with the concentration of up to 0.56 mol-Fe/L. Different from conventional studies under diluted conditions with pH control, the dissolution followed a non-reductive mechanism, producing [Fe³⁺HC2O4]²⁺ as a dominant iron species, and highly correlated with a concentration of proton in the solution. The experimental results and proposed stoichiometries identified a minimum amount of oxalic acid required for the complete dissolution of iron oxide independently from the concentration and type of loaded iron oxide. Among iron oxides tested (α-Fe2O3, FeOOH and Fe3O4) as the feedstock, Fe3O4 had an advantage in the dissolution rate, but showed a relatively low iron recovery in the solution (80–90%) because of an unavoidable formation of FeC2O4·2H2O precipitates.
... However, direct discharge of the slags without treatment not only causes environment pollution problems, but also leads to a great waste of a useful material resource. At present, there have some researches which focus on recovery or removal of iron from the Fe-containing slags or minerals by leaching or direct reduction [9][10][11], and sulfuric acid [12], nitric acid [13], and oxalic acid [14][15][16][17] were used as reductant, or by oxidation [18] and, roasting [10,19]. By way of contrast, oxalic acid has a strong acidity, good chelating ability to iron, and higher environmental benignity [20,21]. of contrast, oxalic acid has a strong acidity, good chelating ability to iron, and higher environmental benignity [20,21]. ...
Article
Full-text available
Pyrolusite leaching slag is a Fe-containing slag generated from pyrolusite leaching process with SO2. Recovery of iron from the slag not only has economic benefit, but also prevents the secondary pollution to the environment. A novel lab-scale cyclic process for recovering iron from pyrolusite leaching slag was introduced. The process contains two steps: (1) iron was leached with oxalic acid and [Fe(C2O4)n](3−2n)+ solution was generated; (2) the [Fe(C2O4)n](3−2n)+ solution was irradiated by ultraviolet and ferrous oxalate precipitation were obtained. The effect of operation parameter on leaching and irradiation process were studied separately. In the leaching process, the optimal solid/liquid ratio, oxalic acid concentration, leaching temperature, stirring rate, and leaching time are 1:50, 0.40 mol/L, 95 °C, 300 r/min, and 3 h, respectively. In the irradiation process, the best irradiation wavelength, Fe/oxalic acid molar ratio and irradiation time are 254 nm, 1:4, and 30 min. Besides, a test of 9 continuous cycles was carried out and the performance and material balance of the combined process were investigated. The results showed that the cyclic process is entirely feasible and prove to be stable producing, and ferrous oxalate of 99.32% purity. Material balance indicated that 95.17% of iron was recovered in the form of FeC2O4·2H2O, and the recovery efficiency of oxalic acid was 58.52%.
Article
As a mineral resource, due to its stable physical chemistry properties, quartz has a wide range of uses, such as silica glass, silica ceramics, silicon metal in the semiconductor field, solar cells in the photovoltaic field, silica fiber in the fiber-optic communication field, and so on. These applications have the participation of high-purity quartz. The purification of high-purity quartz is an important field for quartz. However, it is very difficult to further purify quartz into high-purity quartz, or even ultra-high-purity quartz, which the cost will increase accordingly. Nevertheless, high-purity quartz in the field of high-tech applications is more prominent, its value will be greatly enhanced. In this review, by introducing the resources and application distribution of high purity quartz, and comparing with the import and export in the world, it is concluded that quartz has a good future for development; by introducing the types of quartz ores and the characteristics of impurities and combining with the most advanced purification technology at present, a reference is provided for the following improvement of purification technology. In addition, the mechanisms are summarized for different purification techniques to explore the more effective techniques for quartz purification and its potential application prospects are described in the future. In this paper, in order to know the present situation and development prospect of resources, technology and application in quartz, its resource, characteristic, purification, and application are reviewed.
Article
In the present work, Natural powder quartz (NPQ) ore was purified based on an integrated approach involving a reductive roasting pretreatment and acid leaching technology. The reductive thermal pretreatment was carried out through roasting in the presence of ammonium sulphate (AS). Compared with the conventional acid leaching technology, the content of iron remaining in concentrate could be reduced to below 0.3 μg·g⁻¹ from 145.2 μg·g⁻¹ after roasting in the presence of AS followed by acid leaching at room temperature. Thermogravimetric-mass spectrometry (TG-MS), colour responses of quartz and Density Functional Theory (DFT) were used to investigate the activation mechanism of iron by roasting with AS. It is inferred that SO2 was acted as a reducing agent which promoted the reduction of Fe (III) to Fe (II), which would facilitate the removal of trace iron impurity from NPQ. This study gives a new insight into the activation and removal mechanism of iron impurity from NPQ by reductive action.
Article
Desorption of Cs⁺ from biotite using various organic and inorganic acids was evaluated considering the removal of Cs⁺ from contaminated soils. Oxalic acid was most effective in desorbing Cs⁺ from biotite. The desorption efficiency increased with heating temperature and time, and 94.8% desorption efficiency was obtained at 85 °C after 4 h. The contents of Al, Fe, and Mg in biotite decreased with the increasing heating time, and these contents decreased by 50%, 91%, and 95%, respectively after 4 h of oxalic acid treatment. In addition, X-ray diffraction could not detect biotite peaks after oxalic acid treatment. The results indicate that oxalic acid desorbed Cs⁺ from biotite by decomposing the biotite structure. Moreover, a desorption efficiency of Cs⁺ from biotite of > 95% was obtained using oxalic acid treatment even in the biotite with aging of 3 months. Since the research on effective desorption of Cs⁺ around the boiling point of water is limited, the results of this study are expected to contribute to the development of low energy and environment-friendly remediation of soil contaminated with radioactive species.
Article
Trace elements in quartz, especially iron impurities, can severely affect the quality of products. The removal of iron impurities is one of the technical difficulties in the preparation process of high-purity quartz sand. In this work, the effect of the transformation of the crystal structure on the removal of iron impurities in quartz sand was investigated. After respectively roasting at 600 °C, 900 °C, and 1200 °C for 4 h, the crystal structure of quartz was transformed, and the target crystal structure was solidified via quenching to form a structure favorable for the removal of iron by acid leaching. The experimental results show that the transformation of the crystal structure can effectively improve the removal efficiency of iron impurities. The content of β-quartz was found to be as high as 94.7% after roasting at 900 °C for 4 h. The removal efficiency of iron impurities reached 98.7% after acid leaching at 200 °C, and the removal efficiency of the total impurities reached 88.2%. In addition, the influences of different crystal structures on the removal of iron impurities were systematically investigated. This work provides excellent practical support for the removal of iron impurities during the preparation of high-purity quartz sand.
Article
Full-text available
The production and distribution of quartz sand for the simplest uses as filters and absorbents, foundry sand, fillers, or abrasives and finally the high-tech industry is first discussed. A special category of ultra-pure quartz is the high quality and high value of experimental glassware in synthetic and analytical chemistry. Information about other high tech products of ultrapure, high added value quartz, particularly optical fibers, silicon manufactured for use in electronics industry and photovoltaic cells is presented next. The mineralogy and natural quartz sources as raw material in industry is described pointing out the alternative uses by the natural and industrial attendant and competitor of quartz, feldspars. With reference to the above basic data of the Greek and international raw quartz production we introduce an ultra-pure quartz production network able to produce finished high-tech products. Useful economic conditions and market design is further developed by discussing economic demands. supply and product quality. We collect primary information, possible sources and relevant representative methods of the industries concerned with ultra-pure quartz leading edge industry. Important companies of ultra-pure quartz and secondary manufacture marketing are listed according to their products of house ware, electronics, optical fibers, efficient solar cells, specific technology of thin films, and integrated circuits for the computer industry.
Article
The total world annual production of kaolin (china clay) is about 18 million tonnes (Watson, 1982a). In 1981 the U.K. production was 2.6 million tonnes and that in the USA was 5.2 million tonnes of which about 90% was produced in Georgia (Coope, 1979; Harben, 1979). In Europe and in North America uses in paper dominate in terms of both tonnage and value. Some 78% of the U.K. production is used as a filler and as a coating pigment in the production of paper, followed by about 15% in the production of ceramic ware with the balance used mainly in paint, plastics, and rubber.
Article
This work aimed at analyzing quartz lumps rejected from a major metallurgical grade silicon producer and at studying the effect of several processing techniques over its purification. The final objective was to enable the use this lumps as raw material for silica glass production. Chemical analyses using ICP-MS technique were conducted to understand the nature of the chemical impurities in the rejected lumps, aiming to identify rather if the impurity was inside or outside the quartz lattice. The processing procedures were divided in two steps, the first consisting of only a physical treatment and the second one consisting of a chemical treatment. The physical treatment consisted of washing, milling (and separating the material by its particle size) and magnetic separation. This treatment reduced most of the impurities present in quartz, purifying over 90% of the Fe contamination and over 60% of the Al contaminations, but it was incapable of producing a powder with similar chemistry to commercial raw materials. The chemical treatment was conducted using two different acid mixtures (dilute HCl and dilute HCl + HF). Interesting results were obtained using the HF containing mixtures. These mixtures were able to produce a powder with commercial purity (with Al impurities lower than 50 ppm). This treatment was also able to reduce lattice impurities.
Article
The impurities removed from the vein quartz sands were investigated with six complexing agents (citric, oxalic, acetic, humic acid, EDTA and thiourea). So as to optimized the leaching reaction parameters and to reach a high rate of impurities removal, the kinds and concentration of complexing agents, reaction temperature and time were also discussed. The results shown that the impurities can be dissolved very effectively by both oxalic acid and acetic acid, and then, the citric, humic acid, EDTA and thiourea can also be increased partly rate of impurities removal. At the same time, the interior impurities of the vein quartz sands has been dissolved out that primary depended on the mixed acids which were 2.0M HCl, 0.5M HF, and 0.8M oxalic acid complexing agent at 80°Cfor 8h. The removal rate of elements Fe, Al, K, Na, Ca, and Mg were respectively 93.31, 47.06, 17.28, 28.82, 12.58 and 62.44 percent.
Article
Considerable evidence indicates that dissolved transition metal ions (TMI) are capable of catalyzing oxidations in atmospheric water droplets, at least in certain circumstances. Wide variations in the importance of TMI chemistry are expected in these systems because concentrations of transition metals in water droplets range over at least 4 orders of magnitude. In the present work we perform an extensive series of model calculations for TMI chemistry in raindrops. The specific TMI discussed are iron, manganese, and copper. The present treatment is restricted to homogeneous processes, that is, those involving dissolved molecules and ions. Results are presented for studies at pH 3 and pH 4, for both daytime and nighttime conditions. Among the results are the following: (1) At pH 3 and pH 4, Fe(III) is present largely as photosensitive hydroxide complexes. Our model results indicate that under atmospheric conditions the photolysis of these complexes is the primary daytime source of reactive free radicals within the droplets, even at quite low TMI concentrations. (2) TMI complex photolysis is not, of course, operative at night. At those times the presence of TMI continues to control the concentration of free radicals in raindrops through "Fenton type" reactions with hydrogen peroxide, for example, Fe(II) + H2O2 → Fe(III) + OH + OH-. (3) The oxidation of S(IV) to S(VI) by H2O2 is the most important daytime sulfite oxidation process in raindrops, but S(IV) oxidation catalyzed by Mn(II) can be significant under certain conditions, particularly at night or in the winter months. (4) Solution nitrogen chemistry is relatively unaffected by TMI. Its most important daytime chemical process is the (rather inefficient) photodissociation of the nitrate ion, a process which generates ozone (and hence HOx radicals). (5) Organic chemistry in atmospheric water droplets is very sensitive to the presence of hydroxyl radicals. Since OH· production is strongly influenced by catalysis involving iron complexes, the presence of soluble iron is a major stimulus for organic chemical processes (such as the conversion of alkyl aldehydes to carboxylic acids). (6) For cases where S(IV) concentrations exceed those of H2O2 the S(IV) effectively "titrates out" the H2O2. If the H2O2 concentration dominates, however, residual H2O2 remains to initiate a variety of solution oxidation chains, particularly those producing organic acids. The presence of H2O2 in the gas phase thus implies acid production in the aqueous phase, the form of the acid depending upon the particular oxidizable species available. (7) The chemical reactions and rate constants used in the calculations are relatively well determined, but our results are quite sensitive to the assumed concentrations of TMI and other species. Increased attention to measurement of species concentrations in fog, clouds, and rain is therefore indicated.
Article
The effect of alcohols on the dissolution of manganese, calcium, and iron from manganiferous ore is reported. The extractive process was studied in sulphuric acid solution by using glucose as reducing agent. The alcohols were employed in order to evaluate their effect on the leaching performance with and without glucose as reducing agent. Three different alcohols MeOH, EtOH, and n-BuOH, were tested in order to investigate the influence of the organic chain length on the metal dissolution during the leaching process.Two different test sequences were followed. The first one was based on the leaching of manganiferous ore by using glucose as reducing agent and a mixture of alcohol/H2O/H2SO4 as reaction media. In the second one, leaching was carried out by using glucose in the H2O/H2SO4 reaction media and after leaching, the aqueous solution was separated from the solid by filtration. Successively, alcohols were added to the leach liquor.The experimental results of Mn, Ca, and Fe dissolution obtained by using the latter procedure were compared with those obtained in the former one. In both the experimental sequences, methyl alcohol gave better results as compared to ethyl and n-butyl alcohol. MeOH showed a notable negative effect on calcium dissolution, thereby decreasing its concentration with respect to manganese and iron extraction. The effect was larger in the runs performed by alcohol addition to the leach liquor than that obtained in the mixed solvent leaching tests.The decrease in calcium dissolution caused by the presence of alcohol has been analysed and modelled.
Article
The effect of various organic acids viz. acetic, formic, citric, ascorbic, succinic, tartaric and oxalic acids, on the iron removal and the resulting brightness improvement of an iron-stained kaolinitic clay from Kalliyur, Thiruvananthapuram, South India, has been investigated. Oxalic acid was found to give the best results both at room temperature as well as at high temperatures because of its high acid strength, good complexing capacity and reducing power. The reaction parameters such as time, temperature and reagent concentration were optimised. The optimum conditions required for achieving brightness ≥80% were: temperature — 100°C, oxalic acid concentration — 0.1 M and reaction time — 90 min. The leaching tests at room temperature for 30 days improved the brightness from 66.3 to 83.5% ISO. The corresponding iron oxide removal was of the order of ∼80%. The addition of ferrous ions and protons improved the reaction kinetics. The leaching tests carried out on previously beneficiated samples using magnetic separation showed only a slight improvement in brightness indicating that brightness depended more on the surface coated iron oxides rather than on the discrete particles. The effect of acid leaching on the physical properties of the clay such as brightness, plasticity, viscosity, specific surface area and pore volume were compared. The slight increase in the specific surface area and the pore volume are suggestive of removal of the cementing non-crystalline alumina, silica and iron oxides from the clay surface and also due to the resulting delamination to a limited extent. No marked change was observed in the viscous as well as the plastic properties due to the deferration treatments.
Article
Iron-complexes on the surface of minerals may play an important role in Fe dissolution in acidic cloud water containing certain organic ligands, and dissolved Fe serves as a critical nutrient in biogeochemical cycles in certain aquatic systems. As the first step to explore this issue, laboratory experiments were conducted to investigate the effects of oxalate on the dissolution of hematite, with leaching of Fe from oxalate-coated hematite in comparison with pure hematite in oxalate solution. The dissolution of oxalate-coated hematite was measured as a function of dissolution time, loading amount of oxalate and pH. The amount of oxalate adsorbed on hematite at pH 2.4 is greater than that at pH 5, while the amount of adsorption increases with increasing oxalate equilibrium concentration in solution. Adsorption of oxalate on hematite follows the Freundlich adsorption model. The amount of Fe dissolved at pH 2.4 is much more than that at pH 5. In low concentration oxalate solution, the amount of Fe dissolution from hematite is independent of oxalate loading on the surface of hematite. In high concentration oxalate solution, however, a relatively high oxalate loading on the hematite surface releases more Fe relative to low oxalate adsorption density on the surface of hematite when the system reaches equilibrium, suggesting that the high content of Fe(III)–oxalate complexation promotes Fe dissolution. Ferric ion dissolution and adsorbed oxalate leaching in solution as a function of pH are two co-existing processes, and pH ∼2.5 is a critical turning point relating the two processes that occur simultaneously. The fitting of the experimental data from this work to a model indicates that Fe–(oxalate)+ and Fe–(oxalate)2- are predominant species in solution in the pH range of 1.5–4.5 during oxalate-coated hematite dissolution in background electrolyte.
Article
The raw sands from Hohenbocka (Germany) containing iron essentially in pyrite form is used for glass grade sands processing by dump leaching for several weeks followed by attrition and two-stage classification. The analysis of the sands by means of X-Ray Fluorescence Analysis (RFA) showed an average of about 420 ppm Fe. The objective of this investigation was to reduce the processing time and the total iron content below 105 ppm in the sand product for special glass applications. Due to the presence of sulfide and oxide iron at different ratios in raw sands, a combination of chemical and physical methods was investigated. Leaching was carried out at different acid concentrations, followed by surface cleaning by neutral and alkaline attrition, and gravity separation. Additionally, the effect of continuous addition of H2O2 during leaching to remove iron from sands was investigated. Only two days of leaching was required at the initial acid concentration to 25 g/L. After attrition and tabling of leached sands, a product with 84 ppm of iron was achieved. The continuous removal of dissolved metals by adsorption with active carbon could make it possible to reuse the regenerated sulphuric acid for leaching. With recirculation, the quantity of fresh sulphuric acid required was 0.4 kg/t of quartz sand.
Article
The purification of quartz using chemical processes is extremely important for many industries, including the glass, electronic, detergent, ceramics, paint, refractory, and metallurgy industries, as well as for advanced technology products. The purpose of this work was to investigate the removal of iron as an impurity from quartz ores using a chemical leaching method with different reagents.The iron content of the quartz ore sample was 310 ppm, and the iron was in the form of Fe2O3. In the first step, pre-enrichment studies were conducted based on the particle size, and the Fe2O3 content of the quartz ore was decreased to 88 ppm. A statistical design of the experiments and an ANOVA (analysis of variance) were performed in the second step to determine the main effects and interactions of the researched factors, which were the concentration of the leaching reagent (H2SO4, HCl, H3PO4, HClO4, and NTA [Nitrilotriacetic acid]), solid/liquid ratio, leaching temperature, and leaching time. The highest Fe2O3 removal was 86.6%, and a 11.8 ppm Fe2O3 content quartz product with a whiteness index (WI) value of 90.6 was obtained after 120 min of treatment at 90°C with a 10% S/L ratio and 1 M H2SO4.