Respirometry studies of bioleaching of low-grade chalcopyrite ore using six acidophilic strains

Respirometry was used to study the growth and activity of six pure cultures of acidophilic bioleaching strains grown on a concentration series of low-grade chalcopyrite ores under various pH conditions. Sulfolobus metallicus, Acidithiobacillus ferrooxidans, Acidianus brierleyi and Leptospirillum ferriphilum were able to grow on a very low-grade ore (equivalent to 0.1% Cu content). However, the two sulphur-oxidising bacteria Acidithiobacillus caldus and Acidithiobacillus thiooxidans grew poorly on the low-grade ore. Growth rates of all strains, except for perhaps S. metallicus at highest ore grades, displayed growth that was limited by substrate availability on this low-grade ore (0.5% Cu content in the ore). The decrease in solution pH from 3.0 to 1.0 enhanced both the cell growth and Cu dissolution.     

Dissolution behaviour of a Turkish lateritic nickel ore

The atmospheric pressure sulphuric acid leaching characteristics of Adatepe (Eski?ehir, Turkey) laterite ore that has recently been put into operation was investigated. The effects of sulphuric acid concentration (5-95%), temperature (20-95 °C) and time (30-240 min) on leaching were determined by nickel, iron and arsenic analyses. The amounts of Ni, Fe and As in solution were observed to increase with increase of temperature from 20 °C to 70 °C for sulphuric acid concentrations between 5% and 95%. Further increase of temperature to 95 °C showed that the dissolution of Ni, Fe and As were increased until 60% sulphuric acid concentration and over 60% a decrease in the dissolution percentages was observed due to the probable formation of nickel and silicon containing ferric sulphate type compounds that cause nickel loss from the leach solution. Experimental results showed that maximum nickel dissolution of 99.2% at 95 °C could be reached in 120 min of leaching time for a sulphuric acid concentration of 60%. The congruency of Ni dissolution with respect to Fe was found to be congruent over about 25% Ni and 15% Fe dissolution values. XRD analyses on the residues obtained after leaching showed that it was not required to dissolve all goethite phase to reach maximum dissolution of nickel contained in the sample. An activation energy of 30.36 kJ/mole was determined for Ni dissolution showing that leaching is controlled by external diffusion and chemical reactions.     

Improving copper flotation recovery from a refractory copper porphyry ore by using ethoxycarbonyl thiourea as a collector

In this paper, N-propyl-N-ethoxycarbonyl thiourea (PECTU) collector was investigated to concentrate copper minerals from a refractory copper porphyry ore through bench-scale and industrial flotation tests. The flotation results indicated that PECTU had strongly collecting power for copper sulfide minerals and excellent selectivity against iron sulfide minerals under moderately alkaline conditions. Compared with sodium butyl xanthate (SBX), PECTU increased the grades and recoveries of Cu, Au and Mo in the copper concentrates, and performed the flotation separation of Cu/Fe sulfide minerals at cleaner pH ∼10.5 as well as decreased 2/3 lime consumption. The results of UV-visible measurements further demonstrated that PECTU could be used as a high selective collector for copper minerals. The experimentally obtained results have been explained from the structure-reactivity relationship of collector by density functional calculation.     

The effect of flotation and parameters for bioleaching of printed circuit boards

Waste electrical and electronic equipment (WEEE) is currently one of the fastest growing waste streams in the world. Typical for WEEE is the high content of valuable and precious metals, as well as harmful contaminants like halogens, flame retardant chemicals and plastics. Currently, WEEE treatment and metal recovery methods are imperfect, polluting and energy intensive. In this paper, novel treatment possibilities are outlined for printed circuit boards (PCB) utilizing both the flotation separation technique and acid bioleaching. Flotation, conducted after crushing and sieving of PCB, produced two fractions: metal-rich concentrate, which is more suitable for pyrometallurgical treatment than untreated PCB, and metal-poor froth suitable for acid bioleaching. It was seen that especially low pH (1.6), high initial Fe²⁺ concentration (7.8 g/l) and low PCB froth concentration in the bioleaching solution (50 g/l) were beneficial for the rapid and selective dissolution of copper. With these parameters, 99% of copper was solubilized from PCB froth in bioreactor treatment, with Cu (6.8 g/l) and Fe (7.0 g/l) being the only major metallic elements in bioleaching solution.     

Molecular characterisation of the microbial community of a full-scale bioreactor treating Bayer liquor organic waste

Sodium oxalate is an organic impurity produced during the Bayer refining of bauxite as a result of the degradation of humic materials associated with the ore. Physico-chemical oxalate destruction techniques, such as combustion, are often expensive and often pose greater environmental risk than the storage of solid oxalate waste. Biodegradation is a more economical and environmentally friendly way to degrade oxalate, but the microbial communities responsible for oxalate degradation have remained largely uncharacterised. In the present work, the microbial community of a full-scale bioreactor achieving complete degradation of oxalate was characterised using 16S rRNA gene clone libraries followed by phylogenetic analysis of the cloned near full-length 16S rRNA sequences. The community was dominated by species belonging to the α-, β- and γ-Proteobacteria groups. Novel oxalate-degrading bacteria belonging to the genus Halomonas and the β-Proteobacteria group were isolated from the microbial community and are currently being characterised.     

2-mercaptobenzothiazole and derivatives in the flotation of galena, chalcocite and sphalerite: A study of flotation, adsorption and microcalorimetry

The results of flotation, using 2-mercaptobenzothiazole (MBT) and its derivatives, 6-methyl-MBT (MMBT), 6-methyloxy-MBT (MOMBT), 6-propyloxy-MBT (PrOMBT), and 6-pentyloxy-MBT (POMBT) on pure mineral samples showed some important advantages in the flotation of galena at neutral pH and low collector dosages. It has been found that MBT shows a high affinity towards surfaces containing lead and copper but no selectivity. The introduction of a pentyloxy ring substituent led to a change in the adsorption kinetics, as shown by microcalorimetry, and an improvement of the affinity towards galena.The basic mechanism of adsorption of MBT on galena and chalcocite has been studied by thermochemical measurements, showing that the adsorption mechanisms of MBT on both minerals are comparable in the initial step, involving the chemisorption of the collector. At concentrations above monolayer a second surface reaction of MBT on galena has been observed and attributed to an oxidative dimerisation.Comparative experiments on adsorption properties of mercapto-benzo-oxazole (MBO) show the important role of the endocyclic element composition on the sorption process. The endocyclic O-atom in MBO prevents chemisorption on galena whereas strong coordinative bonds will be formed on Cu containing surfaces.     

A preliminary research on acid pressure leaching of pyritic copper ore in Kure Copper Mine, Turkey

The combination of roasting and pressure leaching is an alternative process that offers advantages over conventional processes because of the shorter leaching time and higher metal recovery. The copper and iron sulphide minerals examined in this study were chalcopyrite (CuFeS₂) and pyrite (FeS₂). The best results obtained were with a pre-treatment by roasting followed by acid pressure leaching in an autoclave system. The extraction of copper achieved was over 85%. Copper dissolution in this system is affected by particle size, leaching time and oxygen pressure. This paper presents the preliminary research on acid leaching of pyritic copper ore in an autoclave system under laboratory conditions.     

The generation of toxic reactive oxygen species (ROS) from mechanically activated sulphide concentrates and its effect on thermophilic bioleaching

Two types of laboratory mills, planetary and vibratory, were used to activate sulphide mineral concentrates mechanically before thermophilic (bio)leaching. These samples were analysed in terms of particle size, surface area, density, SEM, XRD line profile analysis and reactivity. The product particle size distributions indicated different particle breakage mechanisms of the two mills. The surface area for pyrite milled with the planetary mill was three fold that milled in the vibratory mill for the same length of time. Planetary milled samples showed lower densities, up to 4% less for pyrite samples, compared to vibratory milled samples. Particle surface oxidation, observed by SEM, occurred post milling. Surface oxidation products were more prevalent with planetary milled sulphide samples. XRD line profile analysis showed more line broadening effects with the planetary mill. This indicated that more bulk particle-related structural defects were present in the planetary milled samples. The reactivity in acidic solution was measured in terms of the generation of toxic reactive oxygen species (ROS): hydrogen peroxide and hydroxyl radicals. The ROS generation from milled sulphides, normalised to constant surface area loading, increased with increased mechanical activation. The planetary milled samples generated greater ROS per sample surface area than vibratory milled samples, more than 4-fold for pyrite after 60 min of milling. Increased ROS generation was postulated to result from increased surface area defects, solubilisation of iron oxidation products and bulk particle-related defects.The effect of mechanical activation on performance on thermophilic leaching and bioleaching tests was investigated using milled samples at 2% (w/v) pulp density. Short mill times improved leach rates from both mills, up to 7-fold cf. unactivated feed leach rates. Poor bioleaching performance resulted following long periods of mechanical activation (20-60 min). Pyrite and chalcopyrite bioleaching performance decreased dramatically above surface area loadings of 25 and 125 m²/L respectively. Planetary milled samples were less amenable to bioleaching. For pyrite milled for 20 and 60 min and chalcopyrite milled for 40 min, no viable cells were observed following inoculation via fluorescence microscopy, suggesting culture death supported by compromised ferrous iron oxidation. The generation of ROS was postulated to cause poor bioleaching performance under these conditions.     

Mixed sulphide-oxide lead and zinc ores: Problems and solutions

Mixed sulphide-oxide lead and zinc ores are most often found in the transition, and occasionally in the oxidised, zones of lead-zinc ore-bodies. They are of great importance because there are numerous unexploited or abandoned reserves of these ores in the world.However they present difficulties for conventional mineral processing due to complex mineralogy. In this paper, the specific problems associated with these types of ores are described and methods for solving these problems, combining economic and technical considerations, are discussed.The results of experiments carried out at laboratory scale are presented, in which the dissolution of mixed ore in sulphuric acid without oxidising agents was investigated. The results show the feasibility of zinc recovery from mixed sulphide-oxide lead and zinc ores, which underlines the potential of this approach. We also propose a conceptual flow diagram for the hydrometallurgical processing of these ores.     

Determination of the relative leaching kinetics of Cu, Rh, Ru and Ir during the sulphuric acid pressure leaching of leach residue derived from Ni-Cu converter matte enriched in platinum group metals

Hydrometallurgical process routes are typically used for separation of platinum group metals (PGMs) from base metals in Ni-Cu converter matte. Nickel dissolution is primarily achieved in the first stage leach (high pressure or atmospheric leaching, or a combination of the two), which is followed by second stage high pressure sulphuric acid/oxygen leaching to dissolve copper and the remaining nickel. PGMs are recovered from the leaching residue, and their dissolution must hence be limited. The leaching of base metals in the first stage has been characterised, but there is a limited understanding of the behaviour of metals, and more specifically PGMs, in the second stage pressure leach. This research presents the results of laboratory work performed to investigate the kinetics of leaching in the second stage pressure leach. The influence of key operating parameters such as the temperature, pressure, and initial acid concentration on PGM dissolution was investigated.     

Stability analysis of a copper tailings dam via laboratory model tests: A Chinese case study

The upstream method is a popular method for raising tailings dams. Currently in China there are more than 12,000 tailings impoundments and almost 95% of them use the upstream method for the construction of the dam. Statistical data has shown that the tailings impoundment is one of the main sources of risk in the mining industry. Failures of tailings impoundments have resulted in the loss of many lives, considerable property damage, and irreversible pollution in downstream areas. Therefore, the safety of tailings management facilities has been of increasing concern to governments and local communities. The management of a conventional tailings storage facility requires the maintenance of a high level of structural stability. Therefore, according to the relevant mine Acts, the mine operators are required to conduct stability analyses for all types of tailings facilities, whether they are new, active, or decommissioned. For the stability analysis of tailings dams, the accurate profile of the tailings dam is very important. The profiles are easily obtained for both active and decommissioned tailings facilities because their data can be collected through field investigations. However, collecting basic data from newly constructed tailings facilities is difficult. In this paper, a laboratory physical model test has been performed. The construction process for new tailings impoundment has been physically simulated in the laboratory, where the tailings particle composition and distribution below a beach, the change of phreatic surface of the dam, and the engineering properties of the tailings of the dam profiles have been measured. A new tailings facility, Yangtianqin tailings impoundment, owned by Tongchang copper mine of Yuxi Mine Co., was used as a case study to illustrate the physical modeling of the tailings dam. In the model test, the geometrical model of pond area was constructed according to the scale factor, λ_L, of 1:200 (model:prototype), and the tailings discharge system was also established, the tailings slurry then being discharged based on the design data. Finally, on the basis of the model test results on profiles, the stability analysis of the tailings dam at different heights was conducted under different conditions. The model test results and stability analysis show that the height of the tailings dam should be less than that originally planned. The original design of Yangtianqing tailings impoundment should therefore be revised for the safety of the tailings impoundment.     

Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria

Polymetallic Cu–Ag ores of the Central European Kupferschiefer deposits are one of the most important sources of copper in Europe. Because the ores are typically complex and often exceptionally fine-grained the development of efficient alternatives to conventional beneficiation strategies are an important target of current research. Biomining – the use of biological components for metal extraction – may offer solutions that are both efficient and environmentally benign. As conventional bioleaching with acidophilic microorganisms is impeded by the high carbonate content of the Kupferschiefer ores, heterotrophic microorganisms and glutamic acid are investigated as a possible alternative in the present study. The focus of this investigation is solely on the recovery of copper from the Kupferschiefer sensu strictu. Bioleaching experiments were carried out using such material from the Polkowice Mine in Poland. This material is marked by high grade (3.8 wt.% Cu), complex ore mineralogy (chalcocite, bornite, chalcopyrite and covellite in significant quantity) and a gangue mineralogy that is rich in carbonate, organic carbon and clay minerals that together form a very fine-grained matrix. (Bio)leaching experiments yield best results when glutamic acid alone is used – reaching copper recoveries up to 44%. Recoveries are consistently lower in experiments in which glutamic acid and microbiological metabolites are both present. The leaching of chalcocite renders the greatest contribution to the copper recovered to the leach solution in all experiments. It can be concluded that glutamic acid solubilises copper efficiently from Kupferschiefer, mainly from chalcocite.     

The influence of composition of nonpolar oil on flotation of molybdenite

With increasing molybdenum ore mining, the difficult to treat ores, i.e., lower-grade and fine-disseminated ores have gradually increased in importance. Kerosene was widely used as the conventional collector of molybdenum flotation all along, but it does not adapt well to the flotation of molybdenite in difficult to treat ores. Meanwhile, kerosene has been cancelled from the manufacture catalogue in China, which makes large refineries no longer produce it, and in turn makes it difficult for a molybdenum flotation plant to purchase kerosene and makes it even harder for kerosene to keep a stable composition. Therefore, many molybdenum flotation plants began to apply diesel oil instead of kerosene as collector for molybdenite. However, the flotation results reveal that diesel oil from different manufacturers or being of different specifications from the same manufacturers has a different effect on the flotation of molybdenite, and pulp temperature has an obvious effect on the flotation efficiency of diesel oil. In pulp temperatures ranging from 10 to 30 °C, the flotation recovery of molybdenite increases with increasing high-boiling component in diesel oil. When pulp temperature is below 10 °C, the flotation recovery of molybdenite is related to the dispersibility of diesel oil, i.e., the proportion of high-boiling and low-boiling component in diesel oil. Therefore, a molybdenum flotation plant should not blindly apply diesel oil instead of kerosene as the collector for molybdenite, but should select diesel oil that is suitable for the properties of its ore. This technical note is helpful to better select the proper collector for a molybdenum flotation plant.     

Selective reductive leaching of oxidised cobalt containing residue

Nickel was selectively leached from an industrial nickel-cobalt Mixed Hydroxide Precipitate (MHP) under mildly acidic, strongly oxidizing conditions. The resulting cobalt rich residues contained 14-21 wt.% Ni, 3-7 wt.% Co and 3-9 wt.% Mn. The selective extraction of nickel and cobalt from these residues was studied using weak acid and weak acid-reductive leaching. Without the reducing agent, nickel preferentially leached. The controlled addition of a reducing agent increased the extent of nickel leaching and solubilised a portion of the cobalt while manganese remained stable in the solid phase. The extent of copper, iron and aluminium leaching was controlled by pH adjustment.     

The efficiency of indigenous and designed consortia in bioleaching stirred tank reactors

The efficiency of bioleaching is dependant on the establishment of an active microbial community. There is debate as to whether an indigenous microbial community is superior to one composed of microbial strains selected for specific physiological traits. The bioleaching efficiency of three microbial communities was studied: the indigenous community of a commercial bioleaching system (KCCL), a reconstituted consortium of the four major organisms which comprise KCCL that had been ‘un-adapted’ through a period of continuous maintenance in synthetic media (KCCR) and a specifically designed consortium of bioleaching organisms (KCCD). Acidithiobacillus caldus was unable to re-establish itself in the reconstituted, un-adapted consortium. However, the bioleaching rate of this consortium improved over time, and its overall performance was very similar to that of the indigenous community. This was despite the absence of an obligate sulfur-oxidising species, which resulted in the generation of substantially less acid. The performance of the designed consortium was poor, and the results implied that bioleaching consortia (mesophiles or moderate thermophiles) cannot be assembled ‘off-the-shelf’, at least not without a substantial period of adaptation.     

The influence of the oxidation state of pyrite and arsenopyrite on the flotation of an auriferous sulphide ore

In this paper, the influence of the oxidation state of pyrite and arsenopyrite on the flotation of an auriferous sulphide ore was investigated by different techniques, including electrode, pulp potentials, DRIFT spectroscopy and microflotation tests. In addition, the gold and sulphide recoveries were also investigate, in a laboratory-scale cell, as a function of pulp potential and reagent concentration. It was verified that the presence of oxidation products on the sulphide mineral surface demands a higher collector concentration in order to achieve a satisfactory sulphide recovery. The electrochemical behaviour of pyrite and arsenopyrite indicated that a nitrogen atmosphere can lead to a low pulp potential, which inhibits the formation of oxidation products, enhancing both the free gold and sulphide recoveries. Although copper sulphate activates even oxidised sulphide surfaces, it does not improve free gold recovery.     

A detailed mineralogical assessment of sphalerites from the Gamsberg zinc deposit, South Africa: The manganese conundrum

The Gamsberg zinc deposit, located in the Northern Cape Province, represents South Africa’s greatest and most important unexploited base metal resource. Yet, in spite of its size, the low zinc grade combined with the high manganese content of the sphalerite continues to prohibit development of the deposit, as the high manganese content makes the zinc concentrates unsuitable for processing by conventional smelting methods, i.e. roasting, leaching/solvent extraction and/or electrowinning.Although numerous published investigations of the Gamsberg deposit have been undertaken, few have focused on the correlation between petrography and mineral chemistry of sphalerite and their implications on mineral processing. In accordance, the aims of this investigation are to highlight the importance of conducting a detailed geometallurgical investigation, as well as provide some new constraints on the metallurgical behavior of sphalerite and zinc concentrates from the Gamsberg deposit. Detailed analysis of sphalerite by petrographic and various microanalytical techniques reveal a marked absence of correlation between crystal morphology and mineral chemistry, necessitating a chemically based classification scheme. As such, six sphalerite populations where identified. They are: zinc-, cobalt-, iron- and manganese-rich, as well as manganese-enriched and manganese-poor. The zinc- and cobalt-rich populations display high zinc contents and low concentrations of iron and manganese, while the iron-rich population displays higher iron contents. Dominating the sphalerites of the mineralized pelitic schist is the manganese-enriched population. Of volumetrically lesser importance are the manganese-poor and -rich populations. The manganese-rich population contains high levels of iron, manganese, cobalt and cadmium relative to the zinc-rich population. In contrast, the manganese-poor population displays similar concentrations of cobalt and cadmium to the zinc-rich population, with iron and manganese intermediate between the zinc- and iron-rich populations.Comparisons between the sphalerite populations and milling size fractions reveal a consistent correlation between sphalerite mineral chemistry and size fractions with the coarser-grained concentrates being economically less favorable compared to the finer-grained concentrates, which display higher zinc contents. Combined with other lines of evidence, this suggests that the sphalerites of mineralized pelitic schist exhibit extensive solid solution that will have an effect on process optimization. For instance, it suggests that milling to a finer grain size will not remove or reduce the iron and manganese content. Another concern to processing will be the variable mineral chemistry of sphalerite, which might cause some sphalerites to display a delayed response during flotation or misreport to the lead concentrate. In spite of this, using solvent extraction, the elevated manganese content of the concentrates could be controlled, while simultaneously recovering zinc and manganese for sale. Hence, the recovery of manganese metal as a by-product could potentially enhance the economics of the deposit. Alternatively, other forms of mineral processing and metal extraction must be evaluated to meet the target grades and recoveries.     

Recovery of heavy metals from MSW molten fly ash by carrier-in-pulp method: Fe powder as carrier

Municipal solid waste (MSW) molten fly ash is classified as a hazardous waste because it contains considerable amount of heavy metals, which pose environmental concern due to their leaching potential in landfill environment. This study proposes carrier-in-pulp (CIP) method as a new hydrometallurgical route to extract and recover Pb, Zn, Cu, and Cd from molten fly ash before landfilling. In this method, a carrier material, which recovers the extracted metals, is added simultaneously with fly ash to a leaching solution and is harvested from the pulp by physical separation method, such as magnetic separation or sieving.To demonstrate the effect of the CIP method, shaking flask experiments were conducted under various conditions using NaCl solution, iron powder as carrier, and molten fly ash. More than 99 wt% Pb, Zn, and Cd, and 97 wt% Cu were extracted from the ash. However, only Pb and Cu were recovered (96.3 wt% Pb and 94.3 wt% Cu) by the iron powder through cementation, leaving behind Zn and Cd ions in the solution phase. The leaching test conducted on the treated fly ash residue revealed that the CIP method suppressed the solubilization of Pb to a value below the landfill disposal guideline.     

Inhibition of acid rock drainage from uranium ore waste using a conventional neutralization and precipitation treatment

Glass columns (length 50 cm, i.d. 4 cm) containing 900 g of uranium ore waste were subjected to a three-step process: (1) acid drainage generation, (2) neutralization and precipitation treatment and, again, (3) acid drainage generation. In the first acid generation step, lasting about one year, different variables (pyrite addition, inoculation and irrigation solution) were tested by measuring effluent pH, redox potential, total iron and sulphate. Conditions of acid generation were satisfactorily reproduced, reaching stable pH values around 2.0 that were determined mainly by pyrite addition and the type of irrigation solution used (distilled water or ferrous sulphate). The neutralization and precipitation treatment consisted of alternating irrigations of a neutralizing solution (CaO saturated plus NaOH) and a precipitating solution (ferric sulphate saturated). This treatment caused accumulation of basic iron sulphate and iron oxide precipitates according to SEM studies. After this treatment, the barrier effect created by the reaction products was checked, using irrigation solutions similar to the first step. The effluents collected showed higher pH and lower redox potential, total iron and sulphate values than those observed before the treatment, evidencing inhibition of acid drainage generation.     

Evaluation of bioleaching factors on gold recovery from ore by cyanide-producing bacteria

The present study was conducted to investigate the gold bioleaching factors from ore by cyanide producing bacterium Chromobacterium violaceum. The optimal condition for cyanide production by C. violaceum was pH 9 and 5 g/L of glycine in YP medium in 2-days of incubation. In shake flask culture, gold bioleaching from the ores by C. violaceum was determined with various experimental protocols such as particle size, pre-grown C. violaceum, pH, and biooxidative treatment. The three types of low grade ores viz., R, S, and H were used. The gold bioleaching efficiencies were recorded as 0%, 50%, and 5% for ores R, S, and H, respectively, when C. violaceum culture was used without any pretreatment (protocol 1). In the experimental protocol involving grinding and pre-grown C. violaceum, leaching efficiencies increased to 60%, 100%, and 40% for ore R, S, and H samples, respectively. Especially, the bioleaching efficiency of ore S enhanced to almost 100% with pre-grown C. violaceum (protocol 2) and that of ore R increased to 53% (i.e., 96% of cyanidable gold) with grinding (protocol 3) due to their mineralogical characteristics of the ores. For refractory gold (i.e., ore R) grinding as pretreatment was needed, and for ore S (almost all of the gold was cyanidable) cyanide production was activated by using pre-grown bacteria. Biooxidation with Acidithiobacillus ferrooxidans and pH adjustment (i.e., 9–11) did not affect the bioleaching efficiencies. The mineralogical cause of gold refractoriness was analyzed by automated SEM that showed most of gold in the ore was entrapped in pyrite and silica. The results indicated that gold bioleaching by C. violaceum from low grade ore can be enhanced by grinding and pre-grown microbe; use of appropriate experimental condition is important according to the mineralogical characteristics.