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Citation: Huang, H.; Li, S.; Gou, H.;
Zhang, N.; Liu, L. Efficient Recovery
of Feldspar, Quartz, and Kaolin from
Weathered Granite. Minerals 2024,14,
300. https://doi.org/10.3390/
min14030300
Academic Editor: Cyril O’Connor
Received: 19 February 2024
Revised: 3 March 2024
Accepted: 11 March 2024
Published: 12 March 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
minerals
Article
Efficient Recovery of Feldspar, Quartz, and Kaolin from
Weathered Granite
Hongjun Huang 1, 2, *, Shihan Li 1,2, Haoran Gou 1,2, Ning Zhang 1,2 and Liming Liu 3
1School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China;
lshyd97@163.com (S.L.); 215612114@csu.edu.cn (H.G.); 225611052@csu.edu.cn (N.Z.)
2Engineering Research Center of Ministry of Education for Carbon Emission Reduction in Metal Resource
Exploitation and Utilization, Central South University, Changsha 410083, China
3College of Chemistry, Xiangtan University, Xiangtan 411100, China; 18074678820@163.com
*Correspondence: 207049@csu.edu.cn
Abstract: Weathered granite contains a high concentration of feldspar, quartz, and kaolin. However,
while it becomes rich in clay due to strong physical weathering, the granite minerals that are not
fully weathered are still very hard, which makes the grinding process more difficult and limits its use.
This study proposes a multi-step process involving grinding, desliming, and flotation to address this
issue. The study determines the appropriate grinding time and power index for the original ore, as
well as the optimal desliming method using a hydrocyclone. To remove iron-containing impurities
like mica, a combination of NaOL/BHA/A CO collectors is used for the reverse rough flotation of
quartz. Additionally, a combination of DDA/SDS collectors is employed to separate quartz and
feldspar through flotation, resulting in a quartz product with a silicon dioxide content of 99.51%. The
objective of efficiently recycling feldspar, quartz, and kaolin from weathered granite is accomplished.
Additionally, the inclusion of intermediate mineral components as by-products of feldspar and raw
materials for aerated bricks is introduced, resulting in the complete utilization of all components.
This innovative approach ensures a clean and environmentally friendly process, eliminating the need
for solid waste disposal.
Keywords: weathered granite; feldspar; quartz; kaolin; recovery
1. Introduction
Weathered granite is a layer of soil formed on the parent rock when granite un-
dergoes intense physical weathering and is affected by impure surface water, such as
rainwater, river water, seawater, and groundwater containing carbonic acid, causing
chemical changes [
1
–
3
]. Its main mineral composition includes clay minerals such as
feldspar (KAlSi
3
O
8
-NaAlSi
3
O
8
), quartz (SiO
2
), mica (KAl
2
(AlSi
3
O
10
)(OH)
2
), and kaolinite
(Al
4
[Si
4
O
10
](OH)
8
) [
4
,
5
]. Feldspar and other minerals with poor weathering resistance
gradually lose their K
+
and Na
+
content under the action of water and carbon dioxide,
forming the clay mineral kaolinite [
6
,
7
]. This creates the characteristics of high clay content
and complex mineral composition in weathered granite [
8
,
9
]. At the same time, these
characteristics also lead to the generation of a large amount of waste, which puts pressure
on the environment [
10
]. Therefore, it is of great significance to conduct experiments and
research on the efficient and comprehensive utilization of weathered granite [11].
Due to its unique geographical location, China has a large amount of weathered
granite that urgently needs to be comprehensively utilized [
12
–
14
]. By using beneficia-
tion techniques, quartz, sodium feldspar, and potassium feldspar can be separated from
weathered granite, removing colored impurities such as mica, iron, and titanium miner-
als [
15
–
17
]. The combination of gravity separation and magnetic separation can reduce the
content of colored impurities [
18
]. Adding flotation to the magnetic separation process can
further reduce the iron content in the granite, as well as remove mica, iron, and titanium
Minerals 2024,14, 300. https://doi.org/10.3390/min14030300 https://www.mdpi.com/journal/minerals
Minerals 2024,14, 300 2 of 15
mineral impurities, resulting in feldspar and quartz concentrates. Flotation can produce
concentrates with fewer impurities compared to magnetic separation, and both methods
can meet the raw material requirements of the ceramic industry. Among them, feldspar
products with an iron impurity content of less than 1% and quartz products with a silica
content of more than 99% meet the sales standards [19–21].
Most of the current studies focus on the valuable components, such as quartz, feldspar,
and mica, that are separated from weathered granite during the sorting process. There are
few studies conducted on the treatment of medium ore, fine-grained slime, and magnetic
concentrate with high iron content [
22
–
24
]. These materials are often discarded as tailings
waste and not fully utilized. This failure to make full use of resources puts greater pressure
on the ecological environment.
In order to utilize the characteristics of weathered granite in Guangdong, this ex-
periment utilizes various combined beneficiation methods such as physical separation,
flotation, and chemical beneficiation to enrich and separate the components of feldspar,
quartz, and kaolin. The process parameters are optimized to determine the best process
flow and ultimately achieve satisfactory laboratory results. Next, the primary product is
tested for improved whiteness to meet the quality requirements of ceramic raw materials.
Performance tests are also conducted to determine the optimal product plan. Finally, a
detailed small-scale experiment is conducted to achieve favorable results and determine the
best product plan. This research has developed technologically and economically feasible
new technologies for the comprehensive utilization of innovative solutions that achieve the
efficient, clean, waste-free, full utilization of all products.
2. Materials and Methods
2.1. Mineralogy and Reagents
In this study, the experimental samples were obtained from Fengsheng Mining Co.,
Ltd. in Guangdong, China. To ensure the representativeness of the experimental material
samples and minimize data errors between the experimental ore and the original material,
the moderately weathered and fully weathered granite were mixed thoroughly using
an XH-III three-dimensional mixer to obtain the comprehensive material sample for this
experiment. Table 1displays the chemical composition of weathered granite. It is evident
that the Al
2
O
3
content is 15.71% and the Fe
2
O
3
content is 1.68%, both of which fail to meet
the required standards for feldspar ceramic materials. Additionally, the SiO
2
content is
64.08%, which also falls below the minimum standards for quartz products. The results
of the XRD analysis in Figure 1indicate that the main mineral components of the original
ore are quartz and potassium feldspar, with a quartz content of about 45%, a potassium
feldspar content of about 25%, a mica content of about 15%, and a kaolinite content of
10%. There is also a small number of amorphous components, mainly due to the loss of
mineral lattice or incomplete crystal cells during weathering, resulting in the presence of
amorphous minerals. In the ceramic industry, the whiteness value of ceramic products
determines their worth. The steps involved in detecting the whiteness of ceramic raw
materials primarily include sample ball mill grinding, crushing, pressing forming, high
temperature setting, and other processes [
25
,
26
]. Subsequently, the whiteness meter is
utilized to measure the whiteness value, which is currently at 22.7%.
Table 1. Main chemical compositions of the weathered granite (wt. %).
Element Al2O3SiO2Fe2O3K2O Na2O TiO2
Content 15.71 64.08 1.68 4.16 0.23 0.21
The granite samples reveal strong mineralogical and textural alterations as a result of
intense physical and chemical weathering, which is expressed by a fine and uneven particle
size distribution [
27
]. In order to further realize the particle size distribution characteristics
of the weathered granite, a particle size screening test was conducted (Table 2). The coarse
mineral particles with a diameter above 4.75 mm are relatively few, with the majority
Minerals 2024,14, 300 3 of 15
distributed above 0.16 mm, accounting for 69.99% of the total content. At the same time,
the content below 0.05 mm reaches 18.33%, indicating a high proportion of fine particles
and a potentially large amount of slime in the original ore of the weathered granite. Impure
iron is mainly concentrated in the fine particle size range, and alumina is also mainly
concentrated in the fine particle size range. This pattern provides a basis for subsequent
iron removal and the production of kaolin products.
Minerals 2024, 14, x FOR PEER REVIEW 3 of 16
Figure 1. XRD and analysis of the weathered granite.
The granite samples reveal strong mineralogical and textural alterations as a result
of intense physical and chemical weathering, which is expressed by a fine and uneven
particle size distribution [27]. In order to further realize the particle size distribution char-
acteristics of the weathered granite, a particle size screening test was conducted (Table 2).
The coarse mineral particles with a diameter above 4.75 mm are relatively few, with the
majority distributed above 0.16 mm, accounting for 69.99% of the total content. At the
same time, the content below 0.05 mm reaches 18.33%, indicating a high proportion of fine
particles and a potentially large amount of slime in the original ore of the weathered gran-
ite. Impure iron is mainly concentrated in the fine particle size range, and alumina is also
mainly concentrated in the fine particle size range. This paern provides a basis for sub-
sequent iron removal and the production of kaolin products.
Table 2. Weathered granite grain size and major components: XRF analysis (wt. %).
Particle Size
Range/mm Fe
2
O
3
SiO
2
Al
2
O
3
K
2
O Content
+4.75 1.74 93.98 20.70 2.94 3.16
4.75~2 1.47 85.83 9.67 2.50 27.83
2~1 1.44 82.50 10.49 4.90 13.86
1~0.42 1.93 74.98 14.43 7.76 16.35
0.42~0.16 2.39 68.07 19.07 9.55 11.95
0.16~0.074 3.22 59.64 25.76 10.26 5.89
0.074~0.05 3.78 56.50 29.92 8.58 2.13
−0.05 4.25 51.33 37.52 5.17 18.33
The data in Table 3 show the results of the iron phase and silica phase analysis of the
weathered granite. Among them, the predominant iron minerals in the rocks are primarily
hematite and limonite, accompanied by a minor presence of iron silicate. Additionally,
trace amounts of magnetite and metallic iron can be found, indicating that weathered
granite is predominantly composed of weakly magnetic iron minerals. The ore exhibits a
high total silica content of 70.19%, with free silica (quar) comprising 42.88% and silicate-
bound silica accounting for 27.31%.
Figure 1. XRD and analysis of the weathered granite.
Table 2. Weathered granite grain size and major components: XRF analysis (wt. %).
Particle Size
Range/mm Fe2O3SiO2Al2O3K2O Content
+4.75 1.74 93.98 20.70 2.94 3.16
4.75~2 1.47 85.83 9.67 2.50 27.83
2~1 1.44 82.50 10.49 4.90 13.86
1~0.42 1.93 74.98 14.43 7.76 16.35
0.42~0.16 2.39 68.07 19.07 9.55 11.95
0.16~0.074 3.22 59.64 25.76 10.26 5.89
0.074~0.05 3.78 56.50 29.92 8.58 2.13
−0.05 4.25 51.33 37.52 5.17 18.33
The data in Table 3show the results of the iron phase and silica phase analysis of the
weathered granite. Among them, the predominant iron minerals in the rocks are primarily
hematite and limonite, accompanied by a minor presence of iron silicate. Additionally, trace
amounts of magnetite and metallic iron can be found, indicating that weathered granite
is predominantly composed of weakly magnetic iron minerals. The ore exhibits a high
total silica content of 70.19%, with free silica (quartz) comprising 42.88% and silicate-bound
silica accounting for 27.31%.
Table 3. The distribution of iron and silicon phases in weathered granite (wt. %).
Iron Phase Type
Fe2+
(Hematite &
Limonite)
mFe
(Magnetic Iron)
MFe
(Metal Iron)
Iron
Silicate
Content 88.98 0.425 0.425 10.17
Silicon Phase Type Free Silicon
Dioxide (Quartz)
Silicon Dioxide
in Silicate
Total Silicon
Dioxide
Silicon Dioxide
Content 42.88 27.31 70.19
Minerals 2024,14, 300 4 of 15
Concerning other physical and chemical properties of the weathered granite, the spe-
cific magnetization coefficient, measured using the LakeShore magnetometer, is
3.2
×
10
−5
, and the Vickers hardness of the raw ore, measured using Innovatest Fal-
con507 equipment, is 783.94, indicating that even after weathering, the ore still has a high
hardness, and the use of steel ball medium is considered for grinding.
The chemical reagents used in this experiment, such as dodecylamine (DDA), sodium
dodecyl sulfonate (SDS), sodium oleate (NaOL), coconut oil amine (A CO), benzohydrox-
amic acid (BHA), sodium silicate, sulfuric acid (H
2
SO
4
), Na
2
CO
3
, NaOH, KCl, sodium
hydrosulfite, and oxalic acid, were sourced from Shanghai Macklin Biochemical Technology
Co., Ltd., Shanghai, China). All of the aforementioned agents were analytically pure. The
tap water used in the experiment was obtained from Changsha city, Hunan province, where
the laboratory is situated.
2.2. Bench-Scale Flotation Tests
The cone ball mill (XMQ, Wuhan Exploration Machinery Co., Ltd., Wuhan, China) was
used for grinding the weathered granite. The hydrocyclone (CZ100, Changsha Mining and
Metallurgy Research Institute Mining and Metallurgical Equipment Co., Ltd., Changsha,
China) was used for desliming. Then, the ultra-fine high-gradient magnetic separator
(DLSD, Yueyang Dali Shen Electromechanical Co., Ltd., Yueyang, China) was used for
magnetic separation, followed by flotation. The single-slot flotation machine (XFD-IV)
(Wuhan Exploration Machinery Co., Ltd., Wuhan, China) was used for Bench-scale flotation
experiments, with a volume of 1 L, impeller speed of 1600 rpm, and slurry density of 28%.
Firstly, we used Na
2
CO
3
as a pH regulator, KCl as a feldspar depressant, and a
combination of NaOL/BHA/A CO as a collector to separate mica and other impurities
containing iron silicate from quartz and feldspar. Then, we used diluted sulfuric acid as
a pH regulator, sodium silicate as a quartz depressant, and DDA/SDS as a combination
collector to float feldspar to achieve the separation of feldspar and quartz [
28
,
29
]. The
concentrate and tailings were filtered, dried, and weighed for analysis.
2.3. Product Evaluation
The products of quartz, feldspar, and kaolin obtained through various tests were
analyzed to judge whether they meet the marketing standards. In the following analy-
sis, we used X-ray fluorescence spectrometers (Axios mAX, Dutch PANalytical Co., Ltd.,
Amsterdam, Dutch) and high-temperature box resistors (WEF.M25/16, Wofu Furnace Co.,
Ltd., Luoyang, China) to test the chemical composition of the conventional nine items. The
whiteness of minerals was analyzed using a whiteness meter (SBDY-1, Shanghai Yuefeng
Instrument Co., Ltd., Shanghai, China). The X-ray diffractometer (X’Pert3 POWder, Dutch
PANalytical Co., Ltd., Amsterdam, Dutch) was utilized for both the mineral composition
and phase analysis. The surface morphology and element distribution of mineral products
were examined using scanning electron microscopy (JSM-IT500, Japanese JEOL, Tokyo,
Japan), energy spectrometer (INCA X-ACT type), and electron probe (EPMA-1600 type).
3. Results and Discussion
3.1. Grinding
The grinding work index is a crucial indicator of ore grindability, and it provides
essential data for accurately determining the mill diameter, medium diameter, and other
key grinding parameters in concentrator design. This test was conducted to obtain the ball
mill work index (WIB). And this was achieved by performing dry closed-circuit grinding
with a ball mill, with the grinding cycle load reaching 250% [
30
,
31
]. The calculation formula
for Wib is as follows:
Wib =4.906
p10.23 ·Gbp 0.82 ·(1
√P80 −1
√F80 )(1)
The variables in the formula are defined as follows:
Wib—Ball mill work index, kw·h/t;
Minerals 2024,14, 300 5 of 15
p1—Test sieve size, µm;
G
bp
—The weight of the newly generated granular material beneath the test sieve with
each rotation of the ball mill, g;
P80—The particle size through which 80% of the material in the product passes, µm;
F80—The particle size of 80% of the material in the mine, µm.
The test equipment used a
φ
305 mm
×
305 mm Bond power index ball mill. The
diameter and quantity of steel balls added to the cylinder during the determination of the
Bond power index are displayed in Table 4. The material sample was mixed and split in
half. It was then dried at a low temperature and crushed to a size of
−
6 mesh (
−
3.35 mm).
A sample of 1.0 kg was taken using the grid subdivision method, while the remaining
crushed material sample was kept for future use. The particle size composition of the raw
ore was determined through screening and analysis. The particle size distribution curve of
the feed is shown in Figure 2a. Based on the grain size sieving curve of the raw ore, the F
80
value is 15.21 mesh, which is equivalent to 977.6
µ
m. The yield of the
−
200 mesh sample
was 17.86%.
Table 4. The diameter and number of steel balls in the cylinder.
Diameter
(mm) φ36.5 φ30.2 φ25.4 φ19.1 φ16 Total
Quantity
(number) 43 67 10 71 94 285
Minerals 2024, 14, x FOR PEER REVIEW 5 of 16
3. Results and Discussion
3.1. Grinding
The grinding work index is a crucial indicator of ore grindability, and it provides
essential data for accurately determining the mill diameter, medium diameter, and other
key grinding parameters in concentrator design. This test was conducted to obtain the ball
mill work index (WIB). And this was achieved by performing dry closed-circuit grinding
with a ball mill, with the grinding cycle load reaching 250% [30,31]. The calculation for-
mula for Wib is as follows:
)
11
(
906.4
8080
82.023.0
1FP
Gp
W
bp
ib
−⋅⋅
= (1)
The variables in the formula are defined as follows:
Wib—Ball mill work index, kw·h/t;
p1—Test sieve size, µm;
Gbp—The weight of the newly generated granular material beneath the test sieve
with each rotation of the ball mill, g;
P80—The particle size through which 80% of the material in the product passes, µm;
F80—The particle size of 80% of the material in the mine, µm.
The test equipment used a φ 305 mm × 305 mm Bond power index ball mill. The
diameter and quantity of steel balls added to the cylinder during the determination of the
Bond power index are displayed in Table 4. The material sample was mixed and split in
half. It was then dried at a low temperature and crushed to a size of −6 mesh (−3.35 mm).
A sample of 1.0 kg was taken using the grid subdivision method, while the remaining
crushed material sample was kept for future use. The particle size composition of the raw
ore was determined through screening and analysis. The particle size distribution curve
of the feed is shown in Figure 2a. Based on the grain size sieving curve of the raw ore, the
F80 value is 15.21 mesh, which is equivalent to 977.6 µm. The yield of the −200 mesh sample
was 17.86%.
Table 4. The diameter and number of steel balls in the cylinder.
Diameter
(mm) φ 36.5 φ 30.2 φ 25.4 φ 19.1 φ 16 Total
Quantity
(number) 43 67 10 71 94 285
Figure 2. (a) Size curve of weathered granite sieve analysis; (b) particle size distribution curve after
balance of product.
The 700 cm
3
material sample was weighed; the weight was 1024 g. The specific gravity
of the sample was obtained: 1024/700 = 1.46 g/cm
3
. The quality of the
−
200 mesh product
in the feed was calculated as follows: sample weight
×
sample yield of
−
200 mesh under
screen = 1024
×
17.86% = 182.87 g. During the measurement, a 700 cm
3
material sample
must be kept in the ball mill, so that the expected product quantity can be calculated.
According to the concept of the work index, the work index was obtained when the
grinding reached 250% of the circulating load, and the expected product quantity was
1/3.5 of the quality of the 700 cm
3
sample. Therefore, the expected product quantity in this
test was 1024/3.5 = 292.57 g. The number of cycles was set at five, and the test data were
measured according to the existing steps (Table 5).
Minerals 2024,14, 300 6 of 15
Table 5. Data of 75µm Bond ball milling power index test of weathered granite.
Cycle
Order
Number of
Revolutions
(r/min)
Mf(g) Mp(g) MO(g) Gbp (g/r)
Circulating
Load (%)
1 200 182.87 396.57 213.70 1.0685 158.21
2 205 72.88 338.35 265.47 1.2950 202.65
3 178 61.81 309.34 247.53 1.3906 231.03
4 169 56.57 292.4 235.83 1.3954 250.21
5 170 53.14 293.2 240.06 1.4121 249.25
The variables in Table 5are defined as follows:
Mf—Material weight under −200 mesh sieve, g;
MP—Mill product weight −200 mesh under screen material, g;
MO—Net grinding production −200 mesh material weight under screen, g;
Gbp—−200 mesh underscreen material weight generated per turn, g.
The balance criterion is judged according to the allowable error of the cycle load and
G
bp
value in the last two cycles. As shown in Table 5, the load for the fourth and fifth cycles
is 250.21% and 249.25%, respectively. The average cycle load is 249.73%. The values for G
bp
are 1.3954 and 1.4121, respectively, with an average G
bp
of (1.4121 + 1.3954)/2 = 1.40375.
Therefore, the error of the Gbp value is as follows:
(maximum −minimum)/average;
=(1.4121 −1.3954)/1.40375 ∗100%;
=1.189% (This value is less than the allowable error of Gbp by 3 %).
The products are mixed evenly under the 4th and 5th -200 mesh sieves. Then, a 200 g
sample is taken using the binomial method for sieving. The particle size curve of the sieved
product after reaching equilibrium is shown in Figure 2b. From the curve, P
80
can be
determined to be 63.92 µm.
From Equation (1), the Bond ball grinding index Wib = 14.79 kWh/t.
A high W
ib
value indicates that the weathered granite has a high hardness and is
a difficult rock to grind. However, the weathered granite contains a high amount of
primary slime. Therefore, the process involves initially using high-frequency vibration
to screen and classify the ore, followed by grinding to prevent excessive grinding. This
method also allows for the selective separation of weathered fine-grained minerals, which
is advantageous for the subsequent preparation of coarse-grained mineral iron removal
and kaolin products. To determine the appropriate grinding fineness, a grinding condition
test is conducted. Five samples, each weighing 500 g and with the primary slime removed,
are subjected to steel ball milling for different durations: 3, 5, 7, 9, and 11 min. The resulting
secondary slime, with a particle size below 0.037 mm, is obtained through re-desliming.
The grind materials are then analyzed, and the results are presented in Table 6. With the
prolongation of grinding time, the number of fine particles increased significantly, and the
content of secondary slime increased significantly due to the dissociation of iron-bearing
minerals during grinding. But the total iron levels also show signs of rising. This may
be caused by the steel balls rubbing against each other during the grinding process to
produce metallic iron. Taking into account the cost and efficiency of actual production and
application in the mine, a grinding time of 7 min is selected as the optimal choice.
Minerals 2024,14, 300 7 of 15
Table 6. Grinding time and test results.
Grinding Time/min −0.074 mm
Content/%
Secondary Mine
Slime Content/% TFe2O3/%
3 57.33 10.23 0.56
5 63.21 12.34 0.73
7 67.23 14.02 0.58
9 69.29 20.24 0.75
11 73.98 24.23 0.68
3.2. Desliming
After the grinding process, a significant amount of slime was produced from weath-
ered granite, which necessitates an efficient desludging procedure [32]. The CZ100 model
high-efficiency hydrocyclone was utilized, featuring a cone angle of 10 degrees and a
column length of 150 mm. This hydrocyclone was primarily employed for desludging and
concentrating fine-grained materials. By adjusting the diameter of the sand outlet of the
hydrocyclone, various desludging effects could be achieved. The overflow pipe diameter is
22 mm, cone angle is 10 degrees, and the feed pressure is 0.2 MPa. Five different conditions
were set for the sand outlet diameter, namely 12 mm, 14 mm, 16 mm, 18 mm, and 20 mm,
and desludging experiments were conducted on weathered granite. The overflow and sand
products were obtained and analyzed using a BT-9300ST laser particle size analyzer, and
the product yield and XRF results were shown in Table 7.
Table 7. Desliming conditions test product yield table.
Serial Number Parameter Product
Concentration/%
Productivity/% TFe2O3/% Al2O3/%
1
d0= 22 mm
ds= 12 mm
P = 0.2 MPa
Overflow 1 2.92 15.79 5.42 0.21
Riffling 1 46.78 84.21 1.74 0.19
Feed 1 13.87 100.00 2.42 14.20
2
d0= 22 mm
ds= 14 mm
P = 0.2 MPa
Overflow 2 3.08 14.30 5.39 0.18
Riffling 2 35.92 85.70 1.80 0.22
Feed 2 14.22 100.00 2.42 14.20
3
d0= 22 mm
ds= 16 mm
P = 0.2 MPa
Overflow 3 3.04 13.28 5.82 0.21
Riffling 3 32.50 86.72 1.64 0.23
Feed 3 14.20 100.00 2.42 14.20
4
d0= 22 mm
ds= 18 mm
P = 0.2 MPa
Overflow 4 2.81 10.40 5.88 0.22
Riffling 4 27.35 89.60 1.89 0.20
Feed 4 14.33 100.00 2.42 14.20
5
d0= 22 mm
ds= 20 mm
P = 0.2 MPa
Overflow 5 2.85 9.67 5.85 0.23
Riffling 5 25.42 90.33 2.26 0.19
Feed 5 14.39 100.00 2.42 14.20
The total size of the feed ore is fine, and the Fe
2
O
3
content is 2.42%, making it suitable
for hydraulic cyclone classification desliming. By comparing the data from Figure 3the
five groups of tests, it can be concluded that the yield of the overflow product, or slime,
decreases as the diameter of the sedimentation port increases. Additionally, the particle
size of the sedimentation product also increases with the increase in the diameter of the
sedimentation port. However, the Fe
2
O
3
content of the sedimentation product does not
show a clear trend. It can be inferred that a larger diameter sedimentation port is not
conducive to effective classification. The desilting yield at 12 mm is 15.79%. Taking into
Minerals 2024,14, 300 8 of 15
account the product yield and the Fe
2
O
3
and Al
2
O
3
content, the best desliming process
condition is selected as a settling mouth diameter of 12 mm.
Minerals 2024, 14, x FOR PEER REVIEW 8 of 16
five groups of tests, it can be concluded that the yield of the overflow product, or slime,
decreases as the diameter of the sedimentation port increases. Additionally, the particle
size of the sedimentation product also increases with the increase in the diameter of the
sedimentation port. However, the Fe2O3 content of the sedimentation product does not
show a clear trend. It can be inferred that a larger diameter sedimentation port is not con-
ducive to effective classification. The desilting yield at 12 mm is 15.79%. Taking into ac-
count the product yield and the Fe2O3 and Al2O3 content, the best desliming process con-
dition is selected as a seling mouth diameter of 12 mm.
Figure 3. Particle size distribution of hydrocyclone products: (a) feed product, (b) overflow 1 prod-
uct, (c) riffling 1 product, (d) overflow 2 product, (e) riffling 2 product, (f) overflow 3 product, (g)
riffling 3 product, (h) overflow 4 product, (i) riffling 4 product, (j) overflow 5 product, and (k) riffling
5 product.
Quar and feldspar products require low iron content, so it is necessary to com-
pletely remove iron impurities, most of which are weakly magnetic ores. It is found that
the high gradient wet magnetic separator with a magnetic induction intensity of 1.5 T
(Tesla) is more excellent for strong magnetic separation. The weathered granite has a small
particle size and high iron content. The effect of the magnetic separation is limited, and
the combination of magnetic separation and flotation can improve the efficiency of bene-
ficiation.
3.3. Flotation Test
Based on the existing studies, the mixed collectors are utilized for the purpose of
separating iron-bearing minerals like mica and hematite from quar and feldspar through
flotation on a 1 L flotation machine. In this particular process, the collector is pre-arranged
and subsequently added to the pulp, as depicted in Figure 4. The study examines the im-
pact of various factors, including pulp pH, NaOL/BHA/A CO mixture ratio, and the
Figure 3. Particle size distribution of hydrocyclone products: (a) feed product, (b) overflow 1 product,
(c) riffling 1 product, (d) overflow 2 product, (e) riffling 2 product, (f) overflow 3 product, (g) riffling
3 product, (h) overflow 4 product, (i) riffling 4 product, (j) overflow 5 product, and (k) riffling 5 product.
Quartz and feldspar products require low iron content, so it is necessary to completely
remove iron impurities, most of which are weakly magnetic ores. It is found that the high
gradient wet magnetic separator with a magnetic induction intensity of 1.5 T (Tesla) is more
excellent for strong magnetic separation. The weathered granite has a small particle size
and high iron content. The effect of the magnetic separation is limited, and the combination
of magnetic separation and flotation can improve the efficiency of beneficiation.
3.3. Flotation Test
Based on the existing studies, the mixed collectors are utilized for the purpose of
separating iron-bearing minerals like mica and hematite from quartz and feldspar through
flotation on a 1 L flotation machine. In this particular process, the collector is pre-arranged
and subsequently added to the pulp, as depicted in Figure 4. The study examines the impact
of various factors, including pulp pH, NaOL/BHA/A CO mixture ratio, and the quantity
of the collector. The grade and recovery rate of iron (Fe) in the tailings are employed as
indicators to evaluate the flotation process.
Minerals 2024,14, 300 9 of 15
Minerals 2024, 14, x FOR PEER REVIEW 9 of 16
quantity of the collector. The grade and recovery rate of iron (Fe) in the tailings are em-
ployed as indicators to evaluate the flotation process.
pH 1min
depressant 2min
Collector 3min
Concentrate
(ferric impurity)
Feed
Quartz Reverse Flotation
Tailings
(quartz&feldspar)
Figure 4. Quar reverse flotation test flow diagram.
Figure 5a illustrates the impact of pulp pH on the recovery and grade of Fe2O3 in
tailings when using a mixed collector of NaOL/BHA/A CO. The other parameters in the
flotation process remain constant: the depressant KCl and sodium silicate are used at 1000
g/t and 300 g/t, respectively, the collector NaOL is used at 100 g/t, BHA at 40 g/t, and A
CO at 1 g/t. As depicted in Figure 5a, within the pH range of 6 to 12, the recovery rate and
grade of Fe2O3 initially decrease and then increase with increasing pulp pH. The removal
of iron-bearing minerals is particularly effective at a pH of 8 to 9, and the iron grade is at
its lowest when the pH is 8.3. Therefore, the optimal pH for quar reverse flotation to
remove iron is 8.3.
Figure 5b shows the impact of different mixtures of NaOL/BHA/A CO on the recov-
ery and grade of Fe2O3 in tailings at a pulp pH of 8.3. The fixed amount of the mixed
collectors is 200 g/t, and other conditions in the flotation process remain constant. It is
evident that as the proportion of sodium oleate increases, the recovery rate and grade of
Fe2O3 decrease significantly. The most effective removal of iron-bearing minerals occurs
when the mixing ratio of NaOL: BHA: A CO is 3:1:0.05, and further increases in the pro-
portion of each reagent worsen the removal effect. Coconut oil amine (A CO), a primary
amine compound commonly used as an emulsifier, can cause pulp flocculation if over-
dosed, thereby affecting flotation effectiveness [33]. Additionally, benzohydroxamic acid
is expensive, so the optimal ratio of the mixed collector is NaOL: BHA: A CO = 3:1:0.05.
Figure 4. Quartz reverse flotation test flow diagram.
Figure 5a illustrates the impact of pulp pH on the recovery and grade of Fe
2
O
3
in
tailings when using a mixed collector of NaOL/BHA/A CO. The other parameters in
the flotation process remain constant: the depressant KCl and sodium silicate are used at
1000 g/t and 300 g/t, respectively, the collector NaOL is used at 100 g/t, BHA at 40 g/t,
and A CO at 1 g/t. As depicted in Figure 5a, within the pH range of 6 to 12, the recovery
rate and grade of Fe
2
O
3
initially decrease and then increase with increasing pulp pH. The
removal of iron-bearing minerals is particularly effective at a pH of 8 to 9, and the iron
grade is at its lowest when the pH is 8.3. Therefore, the optimal pH for quartz reverse
flotation to remove iron is 8.3.
Figure 5b shows the impact of different mixtures of NaOL/BHA/A CO on the recovery
and grade of Fe
2
O
3
in tailings at a pulp pH of 8.3. The fixed amount of the mixed collectors
is 200 g/t, and other conditions in the flotation process remain constant. It is evident that
as the proportion of sodium oleate increases, the recovery rate and grade of Fe
2
O
3
decrease
significantly. The most effective removal of iron-bearing minerals occurs when the mixing
ratio of NaOL: BHA: A CO is 3:1:0.05, and further increases in the proportion of each
reagent worsen the removal effect. Coconut oil amine (A CO), a primary amine compound
commonly used as an emulsifier, can cause pulp flocculation if overdosed, thereby affecting
flotation effectiveness [
33
]. Additionally, benzohydroxamic acid is expensive, so the optimal
ratio of the mixed collector is NaOL: BHA: A CO = 3:1:0.05.
Minerals 2024, 14, x FOR PEER REVIEW 10 of 16
Figure 5. The recovery rate and grade of Fe
2
O
3
varied depending on (a) the pulp pH, (b) the
NaOL/BHA/A CO ratio, and (c) the amount of collector.
When the pH of the pulp is 8.3 and the mixing ratio of NaOL/BHA/A CO is 3:1:0.05,
the influence of the collector amount on the recovery and grade of Fe
2
O
3
in the tailings is
depicted in Figure 5c. The other conditions in the flotation process remain constant, as
mentioned above. It can be observed that as the collector amount increases within the
range of 100–400 g/t, the recovery rate and grade of Fe
2
O
3
continue to decrease. The re-
moval effect of iron-bearing minerals reaches a balance at 300 g/t collector amount, and
the effect of iron removal fluctuates minimally with further increases in the collector
amount. Therefore, the optimal number of mixed collectors is determined to be 300 g/t. In
summary, the best flotation reagent process is when the pH is 8.3 and the dosage of mixed
collector (NaOL: BHA: A CO = 3:1:0.05) is 300 g/t.
The aforementioned tailings were subjected to further flotation. The mixed collector
was used to separate feldspar from quar. Sodium silicate is used as a depressant of
quar. During this process, the collecting agents were added to the ore pulp in the se-
quence of DDA and SDS, as depicted in Figure 6. The effects of various factors, such as
ore pulp pH, DDA/SDS mixing ratio, and collecting agent dosage, were examined, and
the flotation process was assessed based on the grade and recovery rate of the quar prod-
uct.
pH 1min
depressant 2min
Collector 3min
Feldspar Flotation
quartz
Tailings
feldspar
Figure 5. The recovery rate and grade of Fe
2
O
3
varied depending on (a) the pulp pH, (b) the
NaOL/BHA/A CO ratio, and (c) the amount of collector.
Minerals 2024,14, 300 10 of 15
When the pH of the pulp is 8.3 and the mixing ratio of NaOL/BHA/A CO is 3:1:0.05,
the influence of the collector amount on the recovery and grade of Fe
2
O
3
in the tailings
is depicted in Figure 5c. The other conditions in the flotation process remain constant, as
mentioned above. It can be observed that as the collector amount increases within the range
of 100–400 g/t, the recovery rate and grade of Fe
2
O
3
continue to decrease. The removal
effect of iron-bearing minerals reaches a balance at 300 g/t collector amount, and the
effect of iron removal fluctuates minimally with further increases in the collector amount.
Therefore, the optimal number of mixed collectors is determined to be 300 g/t. In summary,
the best flotation reagent process is when the pH is 8.3 and the dosage of mixed collector
(NaOL: BHA: A CO = 3:1:0.05) is 300 g/t.
The aforementioned tailings were subjected to further flotation. The mixed collector
was used to separate feldspar from quartz. Sodium silicate is used as a depressant of quartz.
During this process, the collecting agents were added to the ore pulp in the sequence of
DDA and SDS, as depicted in Figure 6. The effects of various factors, such as ore pulp pH,
DDA/SDS mixing ratio, and collecting agent dosage, were examined, and the flotation
process was assessed based on the grade and recovery rate of the quartz product.
Minerals 2024, 14, x FOR PEER REVIEW 10 of 16
Figure 5. The recovery rate and grade of Fe
2
O
3
varied depending on (a) the pulp pH, (b) the
NaOL/BHA/A CO ratio, and (c) the amount of collector.
When the pH of the pulp is 8.3 and the mixing ratio of NaOL/BHA/A CO is 3:1:0.05,
the influence of the collector amount on the recovery and grade of Fe
2
O
3
in the tailings is
depicted in Figure 5c. The other conditions in the flotation process remain constant, as
mentioned above. It can be observed that as the collector amount increases within the
range of 100–400 g/t, the recovery rate and grade of Fe
2
O
3
continue to decrease. The re-
moval effect of iron-bearing minerals reaches a balance at 300 g/t collector amount, and
the effect of iron removal fluctuates minimally with further increases in the collector
amount. Therefore, the optimal number of mixed collectors is determined to be 300 g/t. In
summary, the best flotation reagent process is when the pH is 8.3 and the dosage of mixed
collector (NaOL: BHA: A CO = 3:1:0.05) is 300 g/t.
The aforementioned tailings were subjected to further flotation. The mixed collector
was used to separate feldspar from quar. Sodium silicate is used as a depressant of
quar. During this process, the collecting agents were added to the ore pulp in the se-
quence of DDA and SDS, as depicted in Figure 6. The effects of various factors, such as
ore pulp pH, DDA/SDS mixing ratio, and collecting agent dosage, were examined, and
the flotation process was assessed based on the grade and recovery rate of the quar prod-
uct.
pH 1min
depressant 2min
Collector 3min
Feldspar Flotation
quartz
Tailings
feldspar
Figure 6. Feldspar flotation test flow diagram.
The effect of pulp pH on the recovery and grade of SiO
2
in quartz products using
a mixed collector of DDA/SDS was investigated. The other parameters in the flotation
process remained unchanged: the depressant sodium silicate was used at a quantity of
300 g/t, the collector DDA was used at a quantity of 60 g/t, and the SDS was used at a
quantity of 40 g/t. As shown in Figure 7a, within the pH range of 2 to 6, the recovery of
SiO
2
initially decreases and then increases with an increase in pulp pH. Similarly, the grade
of SiO
2
initially increases and then decreases. Notably, at pH levels of 2 to 3, there is a
significant enrichment effect on silica, and the highest grade of SiO
2
is achieved at a pH of
2.7. Therefore, the optimal pH for the flotation separation of quartz and feldspar is 2.7.
Figure 7b illustrates the impact of SiO
2
recovery and grade on collector quartz products
made up of different mixing ratios of DDA/SDS when the pulp pH is 2.7. The fixed amount
of the mixed collectors is 100 g/t, and the other conditions in the flotation process remain
constant. It can be observed that the enrichment effect of quartz is more pronounced when
the DDA content is high, indicating a better collection efficiency of DDA and stronger
selectivity of SDS. The highest SiO
2
grade is achieved when the DDA:SDS ratio is 3:1.
Therefore, the optimal ratio for the mixed collectors is DDA: SDS = 3:1.
When the mixed ratio of the mixed collectors DDA/SDS is 3:1 and the pH of the pulp
is 2.7, the influence of the collector amount on the recovery and grade of SiO
2
in quartz
products is studied, as shown in Figure 7c. Other conditions in the flotation process are
kept constant, as mentioned above. It can be observed that within the range of 50 to 300 g/t
collector dosage, the recovery rate of SiO
2
continues to decrease as the collector dosage
increases. Initially, SiO
2
increases, but the curve stabilizes when the dosage reaches 200 g/t.
Taking into account that DDA itself has strong foaming properties, an excessive dosage
will affect the flotation effect [28]. Therefore, the optimal dosage of the mixed collectors is
200 g/t.
Minerals 2024,14, 300 11 of 15
Minerals 2024, 14, x FOR PEER REVIEW 12 of 16
1234567
95
96
97
98
99
100
SiO
2
grade/%
pH
SiO
2
grade
SiO
2
recovery
DDA:60g/t
(a)
SDS:40g/t
36
37
38
39
40
SiO
2
recovery/%
5:1 3:1 1:1 1:3 1:5
94
95
96
97
98
99
100
SiO
2
grade/%
DDA:SDS
SiO
2
grade
DDA+SDS=100g/t
(b)
pH=2.7
34
36
38
40
SiO
2
recovery
SiO
2
recovery/%
Figure 7. The recovery rate and grade of SiO2 varied depending on (a) the pulp pH, (b) the DDA/SDS
ratio, and (c) the amount of collector.
3.4. Comprehensive Recycling Process
On the basis of the above research, further research on the test flow was carried out
to obtain an efficient selection process scheme. Figure 8 illustrates the mass balance chart
for the comprehensive utilization of weathered granite.
For the fine grade raw ore obtained using the high-frequency vibration fine screen,
the magnetic wet separation was carried out twice by using a high gradient magnetic sep-
arator, and the magnetic field intensity was controlled at 1.5 T (Tesla). Kaolin products are
rich in kaolinite, and kaolinite was mainly concentrated in the fine grade raw ore, so fine
grade raw ore was used to produce kaolin products. The product standard of kaolin re-
quires a particle size of less than 800 mesh, while meeting the low iron content. Therefore,
the non-magnetic products needed to be re-ground and modified with 5% sodium bisul-
fite and 5% oxalic acid to obtain qualified kaolin products.
The rough concentrate of quar obtained using reverse flotation contained a large
amount of iron minerals. It was mixed with magnetic products to form a mixture of min-
erals including mica, low-grade feldspar, quar, and iron impurities, which was used as
raw material for aerated bricks, effectively achieving zero-waste production. The feldspar
and quar obtained from four flotation cycles, and with the fine-grade slurry removed by
a hydrocyclone, are mixed together. This product also had a high iron content and was
subjected to magnetic separation using a high-gradient magnetic separator twice, with a
magnetic field intensity of 1.5 T. The resulting magnetic product was also used as raw
material for aerated bricks. The non-magnetic product was then subjected to a rough four-
0 100 200 300 400
98.5
99.0
99.5
SiO
2
grade/%
DDA+SDS
SiO
2
grade
DDA:SDS=3:1
(c)
pH=2.7
33.0
33.5
34.0
34.5
35.0
SiO
2
recovery
SiO
2
recovery/%
Figure 7. The recovery rate and grade of SiO
2
varied depending on (a) the pulp pH, (b) the DDA/SDS
ratio, and (c) the amount of collector.
3.4. Comprehensive Recycling Process
On the basis of the above research, further research on the test flow was carried out to
obtain an efficient selection process scheme. Figure 8illustrates the mass balance chart for
the comprehensive utilization of weathered granite.
For the fine grade raw ore obtained using the high-frequency vibration fine screen, the
magnetic wet separation was carried out twice by using a high gradient magnetic separator,
and the magnetic field intensity was controlled at 1.5 T (Tesla). Kaolin products are rich in
kaolinite, and kaolinite was mainly concentrated in the fine grade raw ore, so fine grade
raw ore was used to produce kaolin products. The product standard of kaolin requires
a particle size of less than 800 mesh, while meeting the low iron content. Therefore, the
non-magnetic products needed to be re-ground and modified with 5% sodium bisulfite and
5% oxalic acid to obtain qualified kaolin products.
The rough concentrate of quartz obtained using reverse flotation contained a large
amount of iron minerals. It was mixed with magnetic products to form a mixture of minerals
including mica, low-grade feldspar, quartz, and iron impurities, which was used as raw
material for aerated bricks, effectively achieving zero-waste production. The feldspar and
quartz obtained from four flotation cycles, and with the fine-grade slurry removed by a
hydrocyclone, are mixed together. This product also had a high iron content and was
subjected to magnetic separation using a high-gradient magnetic separator twice, with
a magnetic field intensity of 1.5 T. The resulting magnetic product was also used as raw
material for aerated bricks. The non-magnetic product was then subjected to a rough
four-stage reverse flotation process to remove iron, resulting in feldspar products and
by-products, which were sold as ceramic raw materials of different grades.
Minerals 2024,14, 300 12 of 15
This production process produced a variety of products including quartz, feldspar,
kaolin, aerated brick raw materials, and feldspar by-products. It maximized the recovery
of valuable components and improved resource utilization efficiency. Next, each product
would undergo a qualification analysis.
Minerals 2024, 14, x FOR PEER REVIEW 13 of 16
stage reverse flotation process to remove iron, resulting in feldspar products and by-prod-
ucts, which were sold as ceramic raw materials of different grades.
This production process produced a variety of products including quar, feldspar,
kaolin, aerated brick raw materials, and feldspar by-products. It maximized the recovery
of valuable components and improved resource utilization efficiency. Next, each product
would undergo a qualification analysis.
Feed
+-
Milling -200 mesh accounted for 67.23%
-+
βK
2
O% βAl
2
O
3
% βSiO
2
% βFe
2
O
3
%Yield %
εK
2
O% εAl
2
O
3
% εSiO
2
% εFe
2
O
3
%
β——grade
ε——recovery
6.05
100.00 17.68 72.96 2.23
7.17 73.55
30.25 49.45 5.64
26.45 13.16 81.24
10.04
11.55 32.21 59.39 2.08 4.82
62.00 9.61 85.52 1.31
12.68
6.48
12.80 29.06 70.31 1.52 4.3949.20 4.55 89.47 1.25
7.60
21.85 7.55 81.46 2.77
0.36
27.35 0.37 99.10 0.039
5.06
18.72 29.55 54.37 0.98
8.28 30.15 57.96 6.61
5.56
1.98 40.40 57.07 22.47
8.62
31.42 14.58 74.88 1.34
8.40 29.05 57.89 7.20
11.4513.81 13.98 72.56 0.79
6.42
17.61 15.03 76.7 1.76
8.44
33.40 16.07 73.83
44.80
46.62
1.82
29.42
19.17
35.71
26.45
13.72
49.43
54.78
45.25
4.40
2.46
31.40 68.6
22.31 39.54
26.12
18.68
8.26
31.28
10.92
14.98 3.28
21.04 33.70
21.04
26.00
12.66
9.33
31.24
35.01
4.53
30.37
17.93
19.28
52.02 82.07
13.95 17.86
13.83
18.42 35.94
9.40 72.67
12.34 60.33
16.31 33.79
1.54
32.25
24.39
1.46
47.98
10.76 37.22
43.95
8.07
9.42 27.80
53.36
27.35
0.45
18.83
13.90
4.93
72.65
Milling
20.53
22.51
38.12
Feed 1.00t/h
13.01 31.95 37.52
15.70 13.97 3.97
7.73
legend：
100.00 100.00 100.00 100.00
High-frequency vibration fine sieve
High gradient
magnetic separation
Modification
Kaolin Products Aerated Bricks
Raw Materials
Feldspar
By-product
Feldspar
Product Quart z
Product
Flotation
Feldspar Flotation
Quartz Reverse Rougher
Desliming
High gradient
magnetic separation
Figure 8. Mass balance chart for comprehensive utilization of weathered granite.
3.5. Product Analysis
The nine routine chemical components are important criteria for testing the quality
of non-metallic raw materials in China. They include the content of LOI (1025 °C), Al2O3,
SiO2, Fe2O3, CaO, MgO, K2O, Na2O, and TiO2 [34]. The analysis results of the five products
are shown in Tables 8 and 9. Among them, the silica content of quar products is more
than 99%, and the whiteness is 95.5, which meets the standard of refined quar sand.
Feldspar products have an iron content of less than 0.5% and a whiteness of 35.9, which is
suitable for the production of glazes and flat glass as high-quality feldspar products. Feld-
spar by-products with an iron content of less than 1% can be used as tertiary feldspar
products for enamel production. The raw materials of aerated brick have a high content
of silicon and iron, which meet the preparation standards of aerated brick. Kaolin has a
high content of aluminum and silicon, and its whiteness is 61.9. In order to determine
whether it meets the product standards of kaolin, a particle morphology analysis is re-
quired.
Table 8. Product chemical composition routine nine items (wt. %).
Product Loss on Ignition (LOI, 1025 °C) Al2O3 SiO2 Fe2O3 CaO MgO K2O Na2O TiO2
quar 0.22 0.23 99.51 0.018 0.01 0.01 0.11 <0.01 <0.01
feldspar 1.49 12.42 76.07 0.46 0.11 0.04 8.63 0.36 0.03
kaolin 9.92 32.54 51.48 2.21 0.14 0.19 4.83 0.15 0.11
Figure 8. Mass balance chart for comprehensive utilization of weathered granite.
3.5. Product Analysis
The nine routine chemical components are important criteria for testing the quality
of non-metallic raw materials in China. They include the content of LOI (1025
◦
C), Al
2
O
3
,
SiO
2
, Fe
2
O
3
, CaO, MgO, K
2
O, Na
2
O, and TiO
2
[
34
]. The analysis results of the five products
are shown in Tables 8and 9. Among them, the silica content of quartz products is more
than 99%, and the whiteness is 95.5, which meets the standard of refined quartz sand.
Feldspar products have an iron content of less than 0.5% and a whiteness of 35.9, which
is suitable for the production of glazes and flat glass as high-quality feldspar products.
Feldspar by-products with an iron content of less than 1% can be used as tertiary feldspar
products for enamel production. The raw materials of aerated brick have a high content of
silicon and iron, which meet the preparation standards of aerated brick. Kaolin has a high
content of aluminum and silicon, and its whiteness is 61.9. In order to determine whether it
meets the product standards of kaolin, a particle morphology analysis is required.
Table 8. Product chemical composition routine nine items (wt. %).
Product
Loss on Ignition (LOI, 1025
◦
C)
Al2O3SiO2Fe2O3CaO MgO K2O Na2O TiO2
quartz 0.22 0.23 99.51 0.018 0.01 0.01 0.11 <0.01 <0.01
feldspar 1.49 12.42 76.07 0.46 0.11 0.04 8.63 0.36 0.03
kaolin 9.92 32.54 51.48 2.21 0.14 0.19 4.83 0.15 0.11
feldspar by-products 1.67 18.74 76.31 0.98 0.23 0.05 6.93 0.54 0.12
aerated brick raw materials
2.32 29.05 57.89 7.2 1.61 0.34 8.4 0.98 0.09
Minerals 2024,14, 300 13 of 15
Table 9. Product whiteness analysis results.
Product Whiteness
quartz 95.5
feldspar 35.9
kaolin 61.9
feldspar by-products 28.3
aerated brick raw materials 2.32
Scanning electron microscopy was utilized to observe the morphology of kaolin
products, as depicted in Figure 9. No iron impurities were detected in the kaolin products,
but there were trace amounts of feldspar carbonate minerals with extremely fine particle
sizes. These minerals were found to be evenly distributed within the kaolinite, resulting
in a high overall kaolinite content. The kaolin particles exhibited a fine plate structure,
indicating a high level of product purity that meets the standards for qualified kaolin.
Minerals 2024, 14, x FOR PEER REVIEW 14 of 16
feldspar by-products 1.67 18.74 76.31 0.98 0.23 0.05 6.93 0.54 0.12
aerated brick raw materials 2.32 29.05 57.89 7.2 1.61 0.34 8.4 0.98 0.09
Table 9. Product whiteness analysis results.
Product Whiteness
quar 95.5
feldspar 35.9
kaolin 61.9
feldspar by-products 28.3
aerated brick raw materials 2.32
Scanning electron microscopy was utilized to observe the morphology of kaolin
products, as depicted in Figure 9. No iron impurities were detected in the kaolin products,
but there were trace amounts of feldspar carbonate minerals with extremely fine particle
sizes. These minerals were found to be evenly distributed within the kaolinite, resulting
in a high overall kaolinite content. The kaolin particles exhibited a fine plate structure,
indicating a high level of product purity that meets the standards for qualified kaolin.
element O Al Si K
content/% 28.05 28.31 40.57 3.06
element O Al Si
content/% 38. 85 26.01 35.15
element O Al Si K
content/% 35.21 26.64 36.62 1.54
Figure 9. Scanning electron microscope and energy spectrum analysis of kaolin products.
Figure 9. Scanning electron microscope and energy spectrum analysis of kaolin products.
4. Conclusions
(1) This study focused on weathered granite as the research object and utilized it as a
resource. Granite possesses characteristics such as a hard and dense texture, high strength,
corrosion resistance, and wear resistance. The study identified high value-added products
that can be utilized in industries such as building materials, composite materials, and
fine ceramics. The various minerals contained in the weathered granite can be effectively
recovered through a composite procedure involving sifting, grinding, desliming, magnetic
separation, and acid-based mixed flotation.
(2) The grinding test revealed that the grinding work index of weathered granite is
14.79 kWh/t, and the optimal grinding time is 7 min. The desliming test indicated that
the ideal desliming process condition is to select a settling mouth diameter of 12 mm for
the hydrocyclone. The flotation tests demonstrated that the best process conditions for the
flotation of iron-bearing minerals, such as mica, from quartz and feldspar are a pH of 8.3, a
mixing ratio of NaOL/BHA/A CO of 3:1:0.05, and a dosage of 300 g/t. The optimal process
conditions for flotation separation of quartz and feldspar are a pH of 2.7, a DDA/SDS
mixing ratio of 3:1, and a dosage of 200 g/t.
(3) The process plan achieves the objective of efficiently recovering feldspar, quartz,
and kaolin from weathered granite. It also ingeniously considers the intermediate value of
mineral components such as feldspar by-products and raw materials for aerated bricks. This
Minerals 2024,14, 300 14 of 15
is a clean and environmentally friendly process plan that makes full use of all components
without any solid waste accumulation. It is expected to bring hundreds of millions of
revenue after it is put into production.
Author Contributions: H.H. conceived of and designed the experiments; S.L. performed the experi-
ments and wrote the paper; H.G. contributed materials; N.Z. and L.L. modified the paper. All authors
have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: Data sharing is not applicable to this article.
Acknowledgments: We are grateful to the Engineering Research Center of the Ministry of Education
for Carbon Emission Reduction in Metal Resource Exploitation and Utilization of Central South
University for technical support.
Conflicts of Interest: The authors declare no conflicts of interest.
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