Mineral Processing and Extractive Metallurgy Review

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Online ISSN: 0882-7508
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Article
The purpose of this study is to test the feasibility of using mixed culture of iron and sulfur-oxidizing bacteria for the dissolution of metals from high-grade zinc and lead sulfide ore. Considering that the roll crusher could reduce the ore size to less than 2 mm, this size fraction was selected in order to study the possibility of removing mill circuit. Effects of parameters such as pulp density, initial pH, Fe2+, oxidation–reduction potential (ORP), and pH fluctuations were investigated, as well. The maximum Zn dissolution was achieved under the conditions of initial pH 2, initial 75 g/L FeSO4 · 7H2O, and pulp density of 50 g/L. The results indicated that under the optimum conditions, about 68.8% of zinc was leached during 24 days of bacterial leaching treatment. The lead recoveries were low (about 1%), because of precipitation of Pb as lead arsenate chloride. Furthermore, the surface studies by using SEM images showed that during chemical leaching the ore dissolution starts from surface discontinuities, but in bacterial leaching all surface becomes involved. In addition, in another process the ore was leached separately with sulfuric acid and sodium hydroxide, and then final results were compared to the bacterial leaching tests in order to find the optimum hydrometallurgical method to extract zinc and lead from these ores.
 
Article
The effects of ultrasonic pretreatment and surface active reagents to improve the efficiency of fine coal dewatering in high frequency vibrating screen have been carried out. The results showed that hydrophobic surface active reagents increased the contact angle and decreased surface tension of the solution reducing the moisture content of fine coal particles. Polyethylene glycol 400 monooleate (PEG-400) was found to be the most effective reagent. Furthermore, when ultrasonic pretreatment was introduced to the fine coal slurry, the residual total moisture content of the fine coal was further decreased.
 
Article
The main goal of this article is to demonstrate an approach based on integration of process simulation and Multi-Objective Genetic Algorithm (MOGA) concepts to solve a real grinding circuit optimization problem by finding the best operating condition under which process objectives can be achieved. Esfordi phosphate plant is located near city of Bafgh at Yazd province of Iran and produces 5 Mt of phosphate annually. The fine particles (nearly −20 µm) in hydrocyclone underflow which contain a high grade of iron are subjected to over grinding. In addition to electrical energy loss, this causes problems in the downstream process, i.e., flotation stage. The main goals of this study were to solve this problem by adjusting operating condition so that (a) hydrocyclone overflow particle size can be increased from 94.2 µm to 100 µm and (b) increase hydrocyclone underflow particle size from 205 to 500 µm. The second process objective will decrease fine particles in hydrocyclone underflow stream. First, plant sampling campaigns were carried out to calibrate ball mill and hydrocyclone models to be used for performing simulation trials. Then, full circuit simulations were done and optimized by MOGA search process to find the best operating condition that produces hydrocyclone overflow and underflow streams with predefined particle sizes simultaneously. The results indicate that there are various solutions that can be recommended for plant testing and performance improvements. The results of plant implementation of one solution for scenario No. 4 showed improved circuit performance and also validated simulator predictions.
 
Article
Iron ore pellets are largely characterized by inherent physical and chemical properties of ore as well as pelletizing conditions including induration time, induration temperature, etc. These parameters essentially vary with types of ores. The production of high-quality pellets from hematite ore is challenging because of high level of fineness (Blaine number) and induration temperature requirement, ensuring severe degradation property during reduction, etc. In this work, the effect of Blaine number (Blaine fineness: expressed as the specific surface area of fines) on the pellets’ properties was studied. The paper presents the effect of Blaine number on green and dry strength, cold crushing strength, reducibility index, reduction degradation index, swelling index, apparent porosity, optical micro structure, etc. of the high alumina hematite ore pellets. The results showed improved properties of iron ore pellets at an optimum Blaine number (2150 cm2/g) but, reduction degradation index was found to be very poor for the given ore. Further investigation showed that when MgO containing flux viz. pyroxenite was added, the reduction degradation index and swelling index of the pellets were improved for identical Blaine number and other optimized process parameters.
 
Article
Experimental work has been conducted on industrial-scale wet comminution devices and hydrocyclone classifiers to investigate the effects of slurry rheology on their performance. Grinding performance is shown to be influenced not only by the absolute value of apparent viscosity and an inferred yield stress, but also by the rheological type of the discharge slurry. A new empirical model of the hydrocyclone incorporating slurry viscosity has been developed. Simulation has shown the effect of increased viscosity on cyclone performance to be generally deleterious.
 
Article
The treating of gold waste rocks in the gold mining industry has grown significantly in the last few years. The operation of a South African gold mining company treating a waste rock dumps with gold content varying between 0.2 to 0.9 g/t with the Commodas optical sorter to minimize the amount of gangue in the waste rock for further treatment was studied. The results obtained showed that the sorting machine has not been operating at the required set targets of 70% gold recovery and Keywords: feed rate; gold; recovery; sorter; waste rocks Document Type: Research Article DOI: http://dx.doi.org/10.1080/08827508.2014.898636 Affiliations: Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Private Bag, Pretoria, South Africa Publication date: March 4, 2015 $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Mining & Metallurgy By this author: Kgaka, M. ; Adeleke, A. A. ; Popoola, A. P. I. ; Olubambi, P. A. GA_googleFillSlot("Horizontal_banner_bottom");
 
Article
Influence of n-dodecane aqueous emulsion on flotation of sulfide minerals present in the copper ore from the Legnica-Glogow Copper Basin (LGOM), carried out on the laboratory scale, was investigated. Five flotation experiments performed in the presence of different doses of n-dodecane were conducted and compared. Next, mineral analysis of selected flotation products were conducted and discussed. The best flotation selectivity was obtained for bornite, tennantite and chalcocite using 600 g/t of n-dodecane. In the case of non-copper sulfides, the maximum selectivity was observed for sphalerite and galena. Measurements of the rest potential of copper sulfide conducted to explain the differences between recoveries of each sulfide mineral were performed. It was observed, that with increasing sulfide rest potential, the recovery was decreasing. The study provided information hitherto poorly available in literature on flotation of sulfides from the LGOM area with n-dodecane.
 
Article
Medium rheology is important to the efficiency of dense medium separation processes. An impediment to the selection of appropriate ferrosilicon products for a given DMS process in the past has been the lack of a consistent and comprehensive set of data describing the rheology of the range of manufactured ferrosilicon products. Rheological tests have therefore been conducted using Samancor ferrosilicon dense media over a wide range of media properties and densities, with a modified Debex online viscometer. The data have been successfully fitted to the MV-model that allows apparent viscosity to be predicted as a function of particle size distribution and shape, and medium density and temperature. The results from this procedure provide the expected viscosity ranges for uncontaminated ferrosilicon dense media slurries.
 
Article
This article reviews the state of the art in processing and extracting ocean manganese nodules. It briefly reviews the mining sites where abundant rich nodules occur and also describes the metal distribution in nodules. The physicochemical characteristics of the nodules, touching upon different facets such as mineralogy, geochemistry, moisture content, and textural properties of the nodules, are discussed in detail. In the extraction aspects of the nodules, is article reviews two different extraction routes often mentioned in the literature during the last two decades, namely hydrometallurgical and biohydrometallurgical treatments. The hydrometallurgical techniques include leaching by mineral acids, ammoniacal leaching, leaching at high temperature, and pressure and leaching with reducing agents. Reduction of manganese dioxide by organics and its probable application in leaching of nodules is described in a detailed manner. The biohydrometallurgy section extensively reviews the bioreduction phenomenon for manganese dioxide and suggests possible application in leaching of nodules. Projected future developments in the field, with an eye on commercialization, are also discussed.
 
The effect of cyanide concentration on extraction of Ag and Au with LIX 7950 (Org.: 0.5% LIX 7950 and 5 g=L 1-dodecanol in n-dodecane; Aq.: [Ag] or [Au] ¼ 4.1 Â 10 À4 mol=L).
The major component in the mixed solution
The distribution isotherms of silver extraction with LIX 7950 (5% v=v LIX 7950 and 20 g=L 1-dodecanol in n-dodecane; CN=Ag ¼ 5.5, pH eq ¼ 10.50 AE 0.05).  
The distribution isotherms of cyanide extraction with LIX 7950 (5% v=v LIX 7950 and 20 g=L 1-dodecanol in n-dodecane; CN=Ag ¼ 5.5, pH eq ¼ 10.50 AE 0.05).  
The distribution constants of metals under different cyanide levels (10% v=v LIX 7950 and 50 g=L 1-dodecanol in n-dodecane; aqueous solution as Table 1; pH eq ¼ 10.50 AE 0.05).  
Article
The cyanidation process is still the dominant technique for gold ore treatment. In this study, the potential use of the guanidine extractant LIX 7950 for recovering silver and gold from alkaline cyanide solution was investigated. The results indicate that LIX 7950 can effectively and efficiently extract silver and gold from their cyanide solution. The extraction of silver and gold with the extractant is favorable at low pH. High cyanide to silver ratio tends to suppress silver loading while cyanide concentration exhibits insignificant effect on gold extraction. The extraction of the mixture solution of metal cyanide complexes with the extractant indicated an extraction sequence of Au >A g > Zn > Ni > Cu > Fe. The loaded silver and gold can be stripped off efficiently with moderate strong NaOH solutions at the presence of small amount of NaCN. The important findings in the research suggest that the extractant can be potentially used to recover silver and gold from alkaline cyanide leachate and the barren cyanide solution from the SX circuit can be recycled to the cyanidation process.
 
Article
Studying dissolution of copper during bioleaching of sulfide-bearing granite rock obtained from Malanjkhand copper mines (Hindustan Copper Ltd.), India, using electron microscopy technique is the main thrust of this investigation. The micron scale examination of metal distribution under electron microprobe at different stages of leaching was studied to interpret the chemical phenomena involved in the transformation process. Bioleaching studies were carried out in vertical columns using acidophilic microorganisms operated at ambient temperature. It was observed that leaching efficiency increased with decrease of particle size and lixiviate flow rate. The electron probe documented the morphological evolution of the granite sample before, after, and during column bioleaching. The feed sample constitutes plagioclase feldspar, orthoclase feldspar, and quartz as major phases. During 15 days of bacterial attack, several disseminated grains appear over the surface leading to surface defects or crystallographic heterogeneity. Formation of a homogenous film over the sulfide was observed after 30 days. Due to increase in grain size with a remarkable increase in thickness of product layer, it slips to the bottom of the column thereby creating barrier for microbial attack and preventing further dissolution.
 
Article
In this work, the contact angles of molybdenite powders in various size fractions (+150 μm, −150 + 75 μm, −53 + 38 μm, −38 + 20 μm, and −5 μm) were determined with the Washburn method by measuring the mass of capillary rise liquids in molybdenite powder beds as the function of time. It was shown that molybdenite powders had a smaller contact angle in superfine size range (−5 μm) than the common size range (+20 μm), which might be attributed to the large decrease of the face/edge ratio on molybdenite surfaces. Also, it has been found that the contact angle of molybdenite particles did not change as the decrease of particle size in the range of +20 μm.
 
Article
Sulfuric acid mist, which is generated in electrowinning tankhouses, poses corrosion problems to the tankhouse structure and adverse health effects to employees. The literature pertaining to the generation of acid mist from bursting bubbles as film and jet droplets is reviewed. In addition, various methods of suppressing acid mist, such as the use of surfactants, balls, and hoods, are presented and discussed. The occupational exposure limits in various countries are presented and the commonly accepted methods of sampling acid mist are reviewed. Data on acid mist from a survey of 25 zinc and copper tankhouses are summarized.
 
Article
This paper presents the results of investigation of the effect of slag composition and the slag basicity, in the process of smelting of sulfide copper concentrate, on the distribution coefficient () for the following elements: Cu, Bi, Co, Au, Ag, Zn, Pb, Ni, As, Sb, Se, and Te. The research was conducted under the industrial operating conditions of the copper smelter in Bor, Serbia. High values for the coefficient of determination (R 2 > 0.6) for the dependence on the slag composition were obtained, which presents a high degree of fitting. In the case of the dependence of on the slag basicity, obtained R 2 values were much lower, due to the much smaller statistical sample.
 
Article
Parallel experimentation allowing comparison of magnetite–hematite–goethite inland and hematite–goethite coastal mill blends in terms of sintering performance is reported. Magnetite–hematite–goethite blend affords slightly lower productivity, tumble index, and yield than hematite–goethite blend. However, magnetite–hematite–goethite blend required 9.2 kg · t−1 lower solid fuel rate than the hematite–goethite blend. The lower sintering temperature of the magnetite–hematite–goethite blend than that of the hematite–goethite blend contributed to higher reducibility and lower low temperature degradation under reduction. Its sinter product also contained lower proportions of columnar silico-ferrite of calcium and alumina, magnetite, and fayalite.
 
Article
Metamorphism of primary manganese deposits changes the oxi-hydroxide assemblage into a braunite-rich paragenesis. Braunite magnetic properties, together with the increase in grain size during metamorphism, can allow magnetic enrichment at gravel-sand grain size. Samples were collected from a manganese deposit in the Eskişehir region of Turkey, where a metamorphic event changed mineralogy from an original Manganese (Mn) oxi-hydroxide and chert assemblage to a braunite-rich quartzite and also showed an increase in grain size as a result of metamorphism. These samples were first crushed to a fine grain size and braunite was collected using a magnetic separator. Results show that metamorphic braunite-rich manganese deposits can be successfully enriched at high Mn recovery with the best results in the +1–10 mm grain size range.
 
Article
In this work, the thermal decomposition of a goethite concentrate from an iron ore concentration plant was studied in order to develop an economic process of preparing porous hematite as an effective adsorbent for the treatment of wastewater containing heavy metals. This study was performed by means of the measurements of X-ray diffraction (XRD), physical adsorption, and thermal gravimetric analyzer (TGA) for the decomposition process and the characterization of the prepared porous hematite. The experimental results showed that the prepared porous hematite mainly consisted of micropores, and considerably increased the specific surface area and pore volume. The mechanism might be attributed to the dehydration and dehydroxylation of goethite in the thermal treatment. It has been found that calcinating temperature was the predominant factor in the preparation of the porous hematite. Also, residence time in the calcinations greatly affected the pore characterization of the porous hematite.
 
Article
Titania-rich slags with 80 mass percent TiO2 are produced in the electric arc furnaces of QIT-Fer & Titane, Inc., by the continuous smelting of hemo-ilmenite ore with anthracite coal. Titania slag represents an important feedstock for the manufacture of titanium dioxide pigment by the sulphate process. Moreover, part of the production of the titania-rich slag is further acid-leached under a high-pressure and moderate-temperature hydrometallurgical process to yield an upgraded titania slag with 94.5 mass percent TiO2, which is used in the chloride process. After describing in detail the beneficiation, chemistry, and mineralogy of the hemo-ilmenite ore, this article reviews the unique crystallochemistry and mineralogy of the titanate phases with pseudobrookite-karrooite structure and to a lesser extent silicates and oxides present in these titania-rich feedstocks, focusing on the chemical reactions occurring at each step of the pyro- and hydro-metallurgical processes. The behavior of major elements such as titanium, iron, magnesium, calcium, aluminum, and silicon along with that of minor elements such as vanadium, chromium, and manganese are particularly detailed. A general discussion of the methods specifically developed for the study of the synthetic minerals present in these materials is also presented.
 
Article
In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe2O3 → Fe3O4 → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe2SiO4 → Fe or FeO → FeAl2O4 → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.
 
Article
An improved method for the modeling of the impurity reduction factor during high-temperature low-pressure silicon treatment is suggested. The implementation of a modified logistic function in a mathematical model allows it to be utilized for any range of treatment temperatures. The new model defines the maximum reduction factor for each impurity element present in liquid silicon and defines a critical treatment temperature value. Evaporation increase constant, with high adaptability for the implementation of new process parameters, indicated rapid increase in impurity removal at treatment temperatures slightly above melting point of silicon. Various statistical parameters for the logistic regression method were considerably lower for the 16 studied impurity elements than for the linear or logarithmic correlations.
 
Article
An experimental study has been carried out to determine the compositions of the slag/matte/metal/tridymite phases in equilibrium in the Cu-Fe-O-S-Si system at 1200℃. The measurements covered the full range of matte compositions from copper-free mattes to white metal, i.e. from 0 to 80 wt% of copper in matte. The research methodology involved high-temperature equilibration, quenching of the samples and accurate measurement of the phase compositions by electron probe X-ray microanalysis. The oxygen concentrations in mattes were directly measured using the EPMA. A comprehensive set of experimental equilibrium data has been obtained for coexisting matte, slag, Cu-Fe metal alloy and Fe-Cu metal alloy phases. It has been shown that solid iron-copper alloys were present at matte grades below 56 wt% Cu, while liquid copper-iron alloys were formed for matte grades higher than 56 wt% Cu. The experimental measurements have been compared with data reported in the literature and the trends calculated using the thermodynamic model descriptions of the system.
 
Article
The main objective of this study is to analyze the evolution of the research in the category ‘Mining & Mineral Processing’. First, we have revised journals that are in this subject category in the database Science Citation Index-Expanded (SCI-E) of the Web of Science (WoS). Second, we have analyzed publications for journals between 1997 and 2012, with an analysis from the perspective of both quantity and quality. To do this, we have analyzed various bibliometric indicators for different countries and research centers such as the number of documents (article and review), showing per document, productivity, the average number of citations, authors, research centers, national and international collaboration including their networks, the weighted and relative impact factor, as well as the h-index. Furthermore, we have analyzed the international dissemination of research of countries through journals and the relationship with the impact factor to detect the published journals of each country. We have also shown that English is the most common language of publication, and the United States is the most productive country, although it has a relatively low impact factor due to the dispersion of its publications in low or medium impact journals. We can also see that University of Science and Technology of Beijing and the Russian Academy of Sciences have been the most productive institutions during the period under study, along with the large increase of the Atomic Energy and Alternative Energies Commission of France (CEA).
 
Article
Microscope-based automated image analysis systems have been used to obtain data regarding mineral liberation. However, this kind of analysis leads to stereological bias due to the intrinsic two-dimensionality characteristic of the technique. Three-dimensional imaging techniques such as X-ray microtomography comes as an alternative method to measure liberation. We explored the potentiality of high-resolution X-ray microtomography to investigate the characteristics of liberation of a Brazilian bauxite. Grade distributions in 2D and 3D were correspondent when all possible cross-sections were considered in 2D. However, 2D surface exposure did not converge accurately to the 3D method due to the loss of 3D information.
 
Article
Density is one of the key factors of coal that provides useful information about its physical and chemical composition. Traditional coal washability analysis is determined by conducting float–sink test, which is time consuming, destructive, and uses environmentally hazardous chemicals. The motivation for this work is to develop a new technique as a rapid, safe, and viable alternative to the current laboratory of float–sink method in order to avoid harmful chemicals and save time. In this study, an alternative technique based on 3D imaging technology called RhoVol in which the density of individual particles is measured by separate mass and volume measurements to determine coal washability curves is introduced. Four different coal samples were taken from the three coal mines (Highveld, Witbank, and Molteno-Indwe) in South Africa. The coal samples (8 + 2.8 mm) were sorted based on density using zinc chloride float–sink procedures (1.2–1.8 g/cm³) and RhoVol. The true densities of each fraction were determined using helium gas pycnometer for calibration of the RhoVol results. After comparing the results of experiments, it was found that the washability curve and ash analysis obtained from the RhoVol technique was in line with the washability produced by the float–sink test. The successful application of RhoVol as a new nondestructive and nontoxic approach to determine coal washability curves and density of separation for coal sorting would allow selecting the most suitable separation method.
 
Article
The effect of chloride ions on the copper extraction equilibria, the rate of extraction, copper/iron selectivity, and chloride extraction was studied for organic phases containing pure ketoxime (LIX 84-IC) and pure nonylaldoxime (LIX 860N-IC). In these systems, the used aqueous phase contained total chloride concentrations from 0 to 110 g/l. It was determined that the chloride ions in the aqueous solution had a large negative effect on the extraction equilibria for LIX 84-IC and a small effect for LIX 860N-IC. This deleterious effect is attributed to an increase in the hydrogen ion activity coefficient in the presence of chloride ions. The chloride accelerated the rate of copper extraction even though the reaction was fast in all the tested conditions. An increase in the temperature from 25°C to 35°C affected positively the extraction equilibria for LIX 84-IC.
 
Article
Gravity separation (jigging) and flotation were used to upgrade barite ore from the under developed Mehdi-Abad deposit with general specific gravity (S.G) 3.59 gr/cm3. Jigging experiments on coarse particles did not indicate significant upgrading (S.G 3.94 gr/cm3 and recovery 90%) where barite particles are mainly liberated in fine size fractions (-175µm). Optimized flotation parameters were selected based on results of designed experiments: Na-dodecylsulphate (collector) 750 g/t, sodium silicate (depressant) 2000 g/t, pH 9, size -106+63µm, conditioning time 4 min. Results of flotation tests based on optimized parameters (S.G 4.31 gr/cm3, recovery 94%) showed substantial improvement in comparison with jigging results.
 
Article
Iron ore pellets abrade during their production and handling, which lowers product quality and leads to dustiness issues. Pellets were collected from a variety of plants (operating either Straight-Grate (SG) or Grate-Kiln (GK) furnaces) to understand whether furnace type affects fines and dust formation. Results showed that pellets fired in SG furnaces were less abrasion-resistant (3.5 × lower) than pellets fired in GK furnaces. Concurrently, laboratory pellets were prepared using various ores, binders, and firing temperatures. These were tested to understand the relationship between abrasion index and dustiness. AI was observed to range from 1 to 14%. Dustiness, determined via AI and size distributions of abrasion progeny, ranged from 0.2 to 1.6%. For AI greater than 5%, AI can be used to indicate potentially high levels of dust. For AI less than 5%, there was a poor correlation between AI and dustiness. This was explained by the observation that as AI decreased, the abrasion product fineness increased. The results from parts I and II of this investigation suggest that material loss and levels of pellet dustiness may be significantly affected by pellet quality up to a certain point. Poorly fired pellets will be dusty during handling and transportation, while well-fired pellets will generate less – but finer – material as their quality improves. This could lead to little observed changes in dust generation over a wide range of pellet quality. Dust generation at each site would then depend on the quantity of material produced and their extent of handling.
 
Article
Thermal decomposition of the mineral sulfide concentrates derived from froth flotation was studied in the temperature range between 1073 K and 1473 K. The experiments were carried out by heating the mineral sulfide concentrates under inert (argon) atmosphere and, in the presence and absence of carbon. The thermal decomposition of the mineral sulfide concentrates were analyzed by plotting the weight loss of the sample against the reaction time which were obtained from the thermogravimeric analysis (TGA) and characterizing the reacted samples by X-ray diffraction (XRD) and microscopic techniques. The extent and rate of thermal decomposition of the samples were temperature dependent. The high sulfur minerals (CuFeS2 and FeS2) were decomposed to low sulfur and stable phases (Cu1.1Fe1.1S2, Cu5FeS4, and FeS). However, the thermal decomposition of the mineral sulfides were complex because of liquid phase formation at high temperature such that the low sulfur phases appear to have precipitated from the liquid phase during cooling of the sample. Metallic copper was produced in the mineral concentrates containing hydrated and carbonated compounds. It was concluded that the formation of copper cannot occur in the absence of internal oxidation in the sample, when the mineral concentrates are heated under inert atmosphere. The phases were compared with the thermodynamic predictions.
 
Article
A simple and useful method to monitor the water content of coal samples using Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is presented. ATR-FTIR analyses of oven-dried and polymer-dried brown coal samples are discussed. The difference spectra indicate that the drying of as-received coal at room temperature using a Super Absorbent Polymer (SAP) removes only 44 % of moisture compared to oven drying at 105 °C. As the SAP does not completely remove the water from the coal the possibility of explosion due to oxidation of the coal powder is greatly reduced. SAP drying is energy and emission efficient compared to oven drying method. At the pH < 5 studied SAP dewatering is dominated by physical processes. The movements in H-bonding observed in ATR-FTIR suggest a physico-chemical process.
 
Article
Cylindrical cavity perturbation method was used to measure complex permittivity of zinc oxide leach residues (ZOLR) at frequency of 2.45 GHz. The results indicate that both dielectric constant and Loss factor of ZOLR increased with increased of temperature and moisture content. The research of ZOLR’s microwave absorption properties were performed based on reflection loss (RL) theory. Microwave absorption peak of ZOLR moves towards higher material thickness with decreasing of moisture content. However, microwave absorption peak of ZOLR moves towards smaller material thickness with increasing of temperature. RL of ZOLR sensitively depends on material thickness of itself. If want to keeping microwave absorption properties of ZOLR greater than 90% in the process of microwave drying, 10mm, 40mm and 50mm should be selected as the optimum material thickness.
 
Article
Plate water absorption has been traditionally used to assess the binding ability of bentonite clay binders for iron ore concentrate pelletization. Until 1997 there was an accepted test by ASTM, but due to inconstant data this method was withdrawn. This value, however, is still used by some pelletization operations to gauge the efficacy of their bentonite. This test procedure has only been investigated on inorganic binders and never organic binders. This paper seeks to confidently prove that PWA can be used to accurately determine the efficacy of starch binders both alone and in conjunction with bentonite. The role of bentonite as a binder for iron ore concentrate is not only to hold agglomerates together during high temperature operations. During pelletization bentonite can mitigate many times its’ own weight in water. This water absorption capacity aids in retarding the growth rate of pellets, as faster growing pellets tend to be weaker. The value of this water absorption, known as plate water absorption (PWA), is used as a metric to determine the strength and quality of the resulting pellets by industrial pelletizing facilities. As new low silica binders seek to replace bentonite they too must take on the role of moisture mitigation. This study has shown that starches with lower water absorption capacities tend to have lower compressive strengths. As the water absorption capacity increases so too does the compressive strength. When using only starch higher absorption capacities lead to lower compressive strengths of pellets exposed to elevated temperatures. When bentonite is used in conjunction with starch, higher water absorption mixtures do exhibit an increase in strength when heated.
 
Article
Due to entrainment or dissolution, organic extractants can contaminate aqueous raffinate during the solvent extraction (SX) process. This study aims to evaluate the effect of conventional SX reagents on the bio-oxidation and metabolism of industrial bacteria. Evaluating the effect of LIX 984N, Chemorex CP 150, D2EHPA, and Acorga M5640 at three concentrations on mesophiles and moderate thermophiles revealed that all extractants reduced the bacterial efficiency at different extents. It was observed that organic phases at 0.02% v/v resulted in a decrement of ferrous iron bio-oxidation rate and a negligible decrease in the bacterial population. At high dosages like 2% v/v, bio-oxidation and bacterial reproduction were utterly disrupted. The oxime-based extractants had a more significant effect on bacteria due to their lower stability and production of toxic substances by hydrolysis. Organic phases more impacted moderate thermophiles at a higher temperature compared to mesophiles. The analysis of Kendall tau-b revealed a strong inter-correlation between the concentration of organic phase and bio-oxidation parameters such as pH, ORP, bacterial population, bio-oxidation rate, and iron precipitation.
 
Article
Advances in the field of mechanical activation of Al-oxyhydroxide minerals (synthetic as well as in natural bauxites) over the years around the globe are described in this review. An overview of fundamental aspects of mechanical activation with select examples of applications/examples in extractive metallurgy preludes the theme, mechanical activation of Al-oxyhydroxides. The focus is primarily on mechanically induced reactivity of largely used (and most commonly available too) Al-oxyhydroxides viz. gibbsite and boehmite. Reactivity, considered in the context of dissolution in alkali solution and transformations during thermal treatment, is reported to increase with mechanical activation. Available information is collaged to answer the question why/how does the observed effects happen. Gaps in the existing knowledge and prospects in Bayer process are also discussed.
 
Article
Potential–pH diagrams for a chalcopyrite–xanthate–H2O and chalcopyrite–NaCN–H2O system at 298 K were constructed to predict depressing components in the flotation of depressed chalcopyrite in cyanidation tailings using xanthate as collector. Sodium hypochlorite, hydrogen peroxide and copper sulfate were used as activators to reduce this depression effect, and the potential–pH diagram for the activator–H2O system was constructed to predict the thermodynamic activating ability. and were dominant in the acidic-to-alkaline region. In alkaline solution, the generation potentials of and are lower than that of CuX. Therefore, they are the main depressing components that influence the flotation of chalcopyrite in cyanidation tailings. In the alkaline region, the oxidative potentials of sodium hypochlorite, hydrogen peroxide and copper sulfate are significantly higher than that of CN-, so CN- is easily oxidized. This results in activation through the loss of hydrophilicity.
 
Article
Thermal decomposition of zinc leach residue has been studied in a tubular furnace under a constant nitrogen gas flowing, at four different operating temperatures (600°C, 750°C, 950°C, and 1150°C). Using a detailed kinetic analysis, it was shown that the investigated process can be described by a two-parameter autocatalytic Šesták–Berggren reaction model. It was noted that the apparent activation energy values Ea increase progressively with a degree of conversion, accompanied by the appearance of a convex Arrhenius dependence. This behavior is a characteristic of a system of parallel competing reactions. It was concluded that the investigated isothermal decomposition process is characterized by unusually very low preexponential factor and low values of the apparent activation energy. Based on the derived density distribution function of Ea values, it was concluded that the isothermal decomposition process probably occurs through four reaction steps, where each step is characterized by one parallel reaction.
 
Article
The leaching kinetics of chalcopyrite is sluggish due to the refractory nature of chalcopyrite and the formation of passive layers. In this study, the effect of mechanical activation on the leaching behavior and mechanism was studied by leaching tests, electrochemical measurements, particle size distribution analysis, scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and electron microprobe. The results show that mechanical activation can greatly promote the chalcopyrite leaching kinetics, and the copper extraction was increased from 14.1% to 55.7% and 91.8% after primary and secondary mechanical activation, respectively. The electrochemical study results indicated that mechanical activation did not change the cathodic reactions kinetics, however, the anodic dissolution kinetics was significantly promoted. XRD and DSC-TGA results show that mechanical activation treatment can effectively activate chalcopyrite due to the grain size reduction, formation of crystal defects and lattice deformation. The main solid product of chalcopyrite leaching is elemental sulfur. Besides particle size reduction, the reduction of grain size, formation of crystal defects and lattice deformation can increase the strain energy and instability of chalcopyrite, which plays an important role in improving chalcopyrite leaching kinetics.
 
Article
Anionic, cationic and cationic/anionic flotation is widely used in the concentration process for low-grade oxidized zinc ores. In the cationic flotation route, sodium silicate is used as a depressant for gangue minerals and amine as a collector for zinc minerals previously activated by sodium sulfide. However, the presence of polyvalent ions in aqueous solution can affect the surface properties of the various minerals and consequently, the selectivity of the process. This study evaluated the effect of Zn, Ca, and Mg ions, originated by the solubility of smithsonite and dolomite, on the surface properties of quartz and hematite. Microflotation tests showed the inefficiency of sodium silicate as a depressant for quartz in aqueous solution even when Zn, Ca, and Mg ions were not present. Activation of hematite by Zn ions was observed, impeding the separation of smithsonite and hematite (iron oxide). Results obtained from the microflotation and zeta potential tests were analyzed based on the speciation diagrams of the reagents and ions studied, as well as published studies.
 
Article
Pig iron nugget process is one of the direct smelting processes developed as an alternative to the traditional blast furnace process. Throughout the process, slag-free pig iron nuggets, which have similar properties to the blast furnace pig iron and white cast iron, are produced by single-stage heat treatment of dried greenballs. During the process, slag separation from the metallized areas can be enhanced by adjustment of the slag’s chemical and physical properties. The objective of this research was to investigate the effects of flux addition rates (basic to acid ratio) to the dried greenball mixture on pig iron nugget production and slag separation. Thus, this study involved the heat treatment of six different greenball mixtures, which contained various amounts of limestone addition (basic to acid ratios, 0, 0.63, 1.02, 1.42, 1.85, and 2.29) utilizing a laboratory-scale resistance box furnace or simultaneous differential scanning calorimetry and thermalgravimetric analyzer. The samples produced by heating in the box furnace were analyzed for their morphological and chemical properties utilizing optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), macroscopic observations, iron titrations, and atomic absorption spectroscopy. It was determined that the highest percentage of iron yield in the nugget for the process and the highest distribution of iron in magnetic slag were obtained when utilizing the greenball mixture, which contained 7.5 wt% limestone as flux (basic to acid ratio of 1.42).
 
Effect of basicity on CCS and RDI of indurated fluxed pellet.
Raw material blend percentages (wt%) for various types of pellets prepared.
Particle size distribution of ground materials.
Green and dry properties of Noamundi ore pellets.
Properties of indurated pellets from Noamundi ore.
Article
Hematite pellet is required to be indurated at very high temperature to achieve its good strength as there is no exothermic heat of oxidation unlike magnetite. As mill scale contains mainly FeO and Fe3O4, any minor amount of its addition in pellet can provide in situ heat and enhance diffusion bonding and sintering. In this study, the mill scale generated in steel plant is added as magnetite input in hematite pellet both in acidic and in basic condition. It has been found that in fluxed pellet, mill scale can improve the properties of pellet. In acidic pellet, the induration temperature has been reduced to a great extent (1250–1275°C) and all properties have been found to be improved due to the addition of 15% mill scale. Mill scale shows enough potential to eliminate the flux addition in producing blast furnace quality pellet from hematite ore. Thus, the flux free acidic pellet has been developed even at very low temperature (1275°C) of induration.
 
Article
Additives play an important role in the recycling of complex refractory iron ore by coal-based reduction to improve the self-sufficiency rate of the ore. In this work, the influence mechanisms of CaF2, Na2CO3, and MgCO3 additives on the coal-based reduction of complex refractory iron ore were studied by x-ray diffraction, thermogravimetry and differential scanning calorimetry, scanning electron microscopy, and energy dispersive spectrometry. The results indicate the three additives could greatly improve the quality of reduction and magnetic separation products. A reduction product metallization degree 93.42%, iron grade 91.23%, and iron recovery 95.48% were obtained under conditions of CaF2 dosage 6%, reduction temperature 1225 °C, and reduction time 50 min. These results were 3.38%, 8.09%, and 0.39% higher, respectively, than could be obtained without additives. The CaF2, and the Na2O and MgO produced by the decomposition of Na2CO3 and MgCO3, could not only replace the FeO from (Mg,Fe)SiO4 and FeAl2O4, but also react with SiO2 and Al2O3 in ore to form their corresponding complex compounds. Moreover, all compounds were benefitted by the increase of the FeO content. The F⁻ ion could replace the O²⁻ ion in the silicon oxygen tetrahedron to reduce the viscosity and surface tension of reduced ore, thus reducing the resistance of iron particle aggregation and growth. In addition, the formation of a local micro melting phase under the action of additives could promote the diffusion of crystalline particles, which is more conducive to the reduction of iron minerals and the formation and growth of iron particles.
 
Article
Although extensive research has been conducted on the effect of water chemistry in flotation, no single study exists which describes the effect of calcium and magnesium on the adsorption of starch onto the hematite in iron ore flotation. In this work flotation, entrainment, zeta potential, and settling tests were performed to determine the differing impact of calcium and magnesium in iron ore flotation. Results showed that magnesium is more detrimental to the flotation process at far lower concentrations than calcium. Performing flotation with 45 ppm of calcium resulted in a comparable impact on the process as performing flotation with 7 ppm of magnesium. While calcium promotes the adsorption of starch onto the hematite and reduces entrainment, past an optimal dosage magnesium is promoting the adsorption of starch to everything in solution causing low grades and recoveries. It was found that the starch adsorption onto the hematite is strongly impacted by the presence of magnesium, suggesting that starch is collecting the magnesium and self-flocculating prior to adsorption onto the hematite. Thus, the presence of magnesium can significantly reduce the flotation performance far more than what would be expected from calcium.
 
Article
Thiosalts are generated as intermediate products in the oxidation of sulfide ores. Thiosalts have relatively low toxicity, however sulfate formed from the degradation of thiosalts, leads to pH depression in receiving water bodies creating toxic conditions for aquatic organisms. Therefore, proper management and treatment of mining effluent water containing thiosalts is critical. This article briefly discusses Acid Mine Drainage (AMD), different sulfur species present in AMD, behavior of thiosalts as a function of pH and temperature, and thiosalt treatment methods including natural degradation, chemical, and biological oxidation. Carbonaceous adsorbents, ion-exchange resins and other adsorbent approaches are discussed in detail.
 
Article
Chalcopyrite flotability were investigated in four common chloride salts. The results indicated that NaCl, KCl, CaCl2 increased chalcopyrite recovery while MgCl2 decreased its recovery. The monovalent salts played an insignificant role while divalent salts apparently decreased the contact angle of chalcopyrite, regardless of the presence of collectors. Furthermore, the zeta potential was increased in divalent salts and even changed from negative to positive values in MgCl2, highly due to Mg(OH)2 precipitation on chalcopyrite surface. In addition, molecular dynamics simulation indicated that Mg(OH)2 precipitates on chalcopyrite (112) surface stabilized the liquid layer and formed a hydrophilic barrier to inhibit SBX adsorption.
 
Article
The adsorption of chelating collector octyl hydroxamate onto malachite was studied at various pH to reveal the adsorption mechanism. Below pH 6, a substantial amount of octyl hydroxamate was consumed by copper ions in solution, leading to low malachite recovery. In the pH range from 6 to 9, octyl hydroxamate mainly existed in the molecular form. The collector reacted with the chemisorbed Cu(OH)⁺ and Cu(CO3)2²⁻ on the malachite surface. The octyl hydroxamate anion was the predominant species above pH 9. The reaction between the anion and the chemisorbed Cu(OH)⁺ and Cu(CO3)2²⁻ on the malachite surface, was responsible for flotation of malachite. At pH 9, the maximum collector adsorption and flotation recovery were achieved, presumably as a result of the coadsorption of octyl hydroxamate molecules and anions. Although Cu(OH)⁺ and Cu(CO3)2²⁻ were the predominant active species for malachite surface below and above pH 8.3, respectively, and octyl hydroxamate anion and molecule were the predominant species below and above pH 9, respectively, the same copper hydroxamate chelate was formed on the malachite surface above pH 6.
 
Article
Weathered crust elution-deposited rare earth ores (WREO) are the most important mineral sources of the middle and heavy rare earth in the world, which are rare earth ions (RE³⁺) adsorbed on clay minerals, such as montmorillonite, kaolinite, etc. In this work, the adsorption mechanism of Lanthanum ion (La³⁺) and Yttrium ion (Y³⁺) on montmorillonite was studied to clarify the interaction between RE³⁺ and clay minerals. The effect of aluminum ion (Al³⁺) on the adsorption behavior of La³⁺ and Y³⁺ was discussed, for the first time, to probe the role of Al³⁺ in aqueous solution and released from clay minerals. With the addition of Al³⁺ in solution, the adsorption capacity of RE³⁺ becomes much lower than that in the single RE³⁺ adsorption system, which indicates the inhibiting effect of Al³⁺ on the RE³⁺ adsorption. No distinct variation on the adsorption capacity of RE³⁺, and hence the more adsorbing sites occupied by Al³⁺ than RE³⁺ were observed at different molar concentration ratio of RE³⁺:Al³⁺ in rare earth (RE)–aluminum (Al) system. Nevertheless, there is a convert of Al³⁺ from adsorption to release at the molar concentration ratio from 1:5 to 1:2 of RE³⁺:Al³⁺ in RE–Al system due to the increasing initial concentration of Al³⁺. Kinetic studies display that the pseudo second-order kinetic model can best describe the RE³⁺adsorption and the Al³⁺release, and the two processes are controlled by chemical reaction.
 
Article
The article makes an effort in consolidating the developments in the field of advanced gravity separation techniques for processing fine particles over the last few decades. The application potentials of various unit operations and the influence of process variables and feed characteristics on the process performance are identified. Fundamentals of advanced gravity separators are discussed from theoretical and applied perspectives. Comparative analyses of various related unit operations are incorporated including the advantages and short falls of different advanced gravity separation techniques. A general guideline is presented that will help designing new mineral processing flow sheets with better efficiency indices.
 
Article
In this review, resources of nickel and status of different processes/technologies in vogue or being developed for extraction of nickel and associated metals from both primary and secondary resources are summarized. Nickel extraction from primary resources such as ores/minerals (sulfides, arsenides, silicates, and oxides) including the unconventional one viz., the polymetallic sea nodules, and various secondary resources has been examined. Though sulfide ores after concentration are generally treated by the pyro-metallurgical route, most processes for lateritic ores deal with either the acid leaching at ambient temperature and pressure, or high pressure, and a few based on the microbial treatment and owing to the extensive research on laterites, a special emphasis is put forth in this review. Prominent sources that are covered in some detail include the solid wastes like spent batteries viz., end-of-life nickel-cadmium (NiCd) and nickel metal hydride (NiMH), spent catalysts, and spent/scrap superalloys, and liquid wastes such as copper bleed stream and electroplating effluents. In particular pre-treatment of the spent nickel-based batteries, leaching of metals from the electrode materials in different lixiviants, besides separation/solvent extraction of nickel/other metals from the leach liquors, are highlighted.
 
Process and material flows diagram of shaft furnace roasting process.
Magnetization roasting process of iron ores in the rotary kiln.
Sketch of the flash magnetization roasting process.
Magnetic separation results of typical refractory iron ores after flash magnetization roasting.
Merits and demerits of different magnetic reduction roasting furnaces.
Article
Improving utilization efficiency of refractory iron ore resources is a common theme for the sustainable development of the world’s steel and iron industry. Magnetization roasting is considered as an effective and typical method for the beneficiation of refractory iron ores. After magnetization roasting, the weakly magnetic iron minerals, including hematite, limonite and siderite, are selectively reduced or oxidized to ferromagnetic magnetite, which is relatively easier to enrich by magnetic separation after liberation pretreatments. The primary magnetization roasting methods include shaft furnace roasting, rotary kiln roasting, fluidized bed roasting, and microwave assisted roasting. This review highlights the developments in magnetization roasting of difficult to treat iron ores, including shaft furnace roasting, rotary kiln roasting, fluidized bed roasting, and microwave assisted roasting in the past decade. Fluidized bed roasting and microwave assisted roasting are considered as the most effective and promising methods, which is essential to be reviewed. Meanwhile, the effective and future magnetization roasting technologies are recommended throughout this review.
 
Article
Magnetite concentrate is typically high in Fe grade and releases extra heat when oxidized to hematite. This will not only improve the sinter quality but also have a potential beneficial impact on the fuel consumption of the sintering process. However, most concentrates are very fine and less reactive, which will negatively impact the green bed permeability and sintering reactions and consequently the productivity of the sintering process. This paper first discusses the effect of magnetite concentrates on the granulation and sintering reactions and then reviews and comments on the technologies recently developed to address the adverse impact of magnetite concentrates.
 
Top-cited authors
Surendra Kawatra
  • Michigan Technological University
Gerald Luttrell
  • Virginia Polytechnic Institute and State University
Roe-Hoan Yoon
  • Virginia Polytechnic Institute and State University
Jan D Miller
  • University of Utah
Timothy Eisele
  • Michigan Technological University