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In this study, the reject fraction of the jaw crusher, located in the first part of the crushing circuit, is used as a considerable stock in copper tank-leaching plant. High market value of copper and ease of practice were the motivating forces on studying the leaching kinetics under controlled conditions. In this regard, first, the influencing parameters such as the acid concentration, solid-to-liquid ratio, agitation speed, particle size, and temperature were assessed on the leaching fraction of copper. The findings showed that the leaching rate is nearly independent of the agitation rate at the high values of 300 rpm. The recovery of copper strongly promoted from 2 to 90% by increasing sulfuric acid concentration from 0.3 to 1.8 M. The increase in the solid-to-liquid ratio and temperature were found to be beneficial as well. Additionally, it was found that above 71% copper could be leached from the reject samples in the size range of 0–2 mm by 0.9 M sulfuric acid after 30 min contact time at 25 °C temperature. In the second stage, the leaching kinetics was studied by shrinking core models to gain a better description of the dissolution process of copper from crushing circuit reject. The results indicated that the dissolution rate could be controlled by both chemical reaction and diffusion process. However, diffusion process was the dominant mechanism in the system investigated. Ultimately, a mixed kinetic model with an activation energy of 11.72 kJ/mol was proposed as the leaching rate-controlling step.

The present study aims at assessing the potential application of CuPRO MEX-3302 in copper extraction from a heap leaching liquor. The role of influential significant parameters, including the leach...

Over the past century, many problems have been focused on the problems of low leaching rate of gold and methods have been developed to intensify the leaching of gold. Among these methods, the use of hydrogen peroxide to accelerate the leaching of gold is known. In order to intensify the leaching process, the indicators of cyanide leaching of gold from ore using hydrogen peroxide were studied. This article presents the results of assay-gravimetric, chemical, and mineralogical analyses of gold-bearing ore from the Sari Gunay Deposit (Iran). The content of sulfide sulfur ore belongs to the category of low-sulphide, by oxidation of sulphur (50.70%) to the category of oxidized ores. Thermodynamic analysis of possible reactions of ore components with hydrogen peroxide is carried out. Laboratory studies on cyanide leaching of gold have shown that the maximum recovery of gold is 52.92% at a concentration of hydrogen peroxide of 0.5%, the recovery of gold without ore treatment is 52.03%. The results of laboratory and column tests with and without treatment with hydrogen peroxide (H2O2–0.5%) were compared. Treatment of gold-bearing ore with hydrogen peroxide during heap leaching of gold increases gold recovery by 1.2% and amounts to 55.89%, without treatment - 54.69%. This increases the consumption of sodium cyanide by 0.04 kg/t.

The widespread introduction of physical and chemical geotechnologies in the production of mineral raw materials makes it possible to involve ores that are poor in the content of the useful component, which are unprofitable to work out using traditional physical and technical methods. One of these new geotechnologies is the heap leaching of rocky uranium ores. When planning the volume of output of finished products, it is necessary to have an analytical apparatus that would make it possible, using the acquired knowledge, to calculate the required volume of mineral raw material production and its varietal composition. Based on their task, studies were conducted on the qualitative and quantitative characteristics of ores that affect the indicators of extraction of useful components from them. As a result of the research, the dependence of the index of uranium extraction into a productive solution during infiltration of sulfuric acid leaching on the material composition of ores was established. Ores localized in various lithological differences of acidic, medium and basic rocks were tested: granites, felsites, trachydacites, andesites and conglomerates. The ores were classified according to the size of the piece with the allocation of fineness classes +200 mm, -200 +150 mm, -150 + 100 mm, -100+70 mm, -70+ 30 mm, -30 mm. The tests were carried out in laboratory and semi-industrial conditions. The maximum extraction was obtained for the class – 30 mm in columns. When leaching in stacks, the maximum extraction of uranium into the solution was obtained for the size class -70+30 mm. The reason for the lower extraction from the -30 mm class during leaching in semi-industrial conditions was the processes of mechanical colmatation, due to the large number of fine fractions. The criterion characterizing the material composition of ores is the content of silica (SiO2). During the tests, the dependence of the uranium extraction coefficient in the productive solution on the content of silica in the ores was established. The higher the concentration of silica, the more uranium passes into the productive solution during leaching with a stable composition of uranium mineralization. The dependence is described by a mathematical formula, which allows us to use it to calculate the extraction of uranium into a productive solution, knowing the material composition of ores

The experience of heap leaching (HL) was analyzed in the following cold climate regions: Alaska, Western regions of the United States, Canada, Kazakhstan, and Russia. The disadvantages of the developed domestic mobile units were uncovered, and the potential for creating HL mobile units was assessed to enable a year-round use of the technology, including in the cryolithozone. The results are presented, which were obtained during investigation of the material composition of the study object, i.e., technogenic gold-containing deposits of the Transbaikal region. The main element content of the mineral raw materials of the technogenic deposits was as follows: Au — 0.35 g/m3, Ag — 3.9 g/m3, SiO2 — 69.3 %, Al2O3 — 15.4 %, Fe2O3 — 5.9 %, CaO — 0.21 %, and MgO — 1.15 %. The phase forms of gold included: cyanidable (intergrown) — 2.3 %, “sealed in quartz” — 13.5 %, “enveloped” — 28.6 %, in magnetite — 55.6 %. A continuous process line was developed, which included the following four unit modules: gravity concentration, first stage of leaching (tank leaching), second stage of leaching (heap leaching), and sorption. The layout of the continuous process line (HL option during the period of subzero temperatures) is provided. The optimal values of the main process parameters of gravity concentration, as well as the first and second stages of leaching have been established experimentally. Prior to tank leaching, an active multiple-reagent solution based on sodium chloride, water and ozone compounds was prepared in a sealed electrochemical reactor. The tank was partitioned into three sections, in which the following operations were carried out in series: chemical opening of the gold-containing minerals; chlorine removal from the geomaterial; and tank leaching of gold. The total duration of heap leaching was 365 days, which was achieved by using two technological options: option 1 (195 days) — classic HL method (from early April to mid-October), option 2 (170 days) — heap leaching in stationary concrete cuvettes using engineering solutions during the period of subzero temperatures (from mid-October to the end of March). A schematic layout of the stationary concrete cuvette constructed in a special way and buried within a 5 to 8 m layer of soil above the ground level with shielding of the upper surface of the stack (heat-insulating covering, clay, large pieces of ore, sulfide rocks) is provided. Product solution drainage was used at various heights, and perforated rigid PVC pipes were used for supplying warm air deep inside the material. The recovery of gold from the technogenic raw materials was increased on average by 27.1 % due to a year-round heap leaching with the use of two technological options: 1 — by 28.7 % (from 58.1 to 86.8 %) using a classic HL method, and 2 — by 27.4 % (from 58.1 to 85.5 %) by using HL in stationary concrete cuvettes. It is proposed to utilize the secondary waste of the HL field (total of five types) in the road-building and construction industries.

The paper provides a theoretical justification of the key chemical aspects of enhancing the process of heap leaching (HL) of gold by using a reagent complex containing hydrogen peroxide. A schematic illustration of heterogeneous catalytic reactions, which occur during metal leaching, as well as examples of the geometry and dissociation energy of a number of gold clusters are presented. The paper provides the results of studying the mineral composition of various types of waste produced by the Darasun mine, including cut-off grade ores of the Talatuy deposits (gold content — 0.7 g/t), mature tailings of the Darasun gold-processing plant (GPP) (gold content — 1.45 g/t), and flotation tailings of the current ore processing at the Darasun GPP (gold content — 0.3 g/t). A process flow diagram is presented to describe the conducted experimental studies of heap leaching of gold from the pelletized granules of technogenic minerals obtained from various types of mining waste. The process of leaching was performed using a reagent complex containing sodium cyanide solution and hydrogen peroxide, which served as a catalyst of the chemical reactions. The conditions that must be met by the geomaterial to be pelletized in order to obtain strong granules and enable gold leaching have been identified. The optimal values of the following key process parameters were determined: grain size of the crushed cut-off grade ore; waste fraction of the pelletized geomaterial (cut-off grade ore : mature tailings : current processing tailings = 1:0.5:0.5); amounts of sodium cyanide and hydrogen peroxide in the leaching solution, which are introduced into the process in stages at a ratio of H2O2 :NaCN = 10:1. An enhancement of the process of geomaterial heap leaching using hydrogen peroxide enables a higher concentration of oxygen in the lower parts of the pile, which results in an increase in gold recovery by 7.6 % (from 79.5 % to 87.1 %) in comparison with the conventional process. The proposed method utilizing physico-chemical geotechnology of gold recovery ensures a sustainable use of the natural mineral resources, as well as a closed cycle of mining production.

Metallurgical & materials engineering 26(2), 199-208 (2020). doi:10.30544/513 special issue: "Hydrometallurgical operations and processes", Published by [Verlag nicht ermittelbar], Belgrade

The effect of high-pressure grinding roll (HPGR) comminution on the physical properties of ore particles and heap leaching of gold was investigated compared with that of conventional jaw crusher co...

Since the cost of gold has increased by an order of magnitude over the past 20 years, gold mining began to be carried out from ores that are not previously acceptable for heap leaching (HL) technology – these are refractory ores with thin and ultrafine inclusions of precious metals, ore with an increased silver content. In the Russian Federation, classical representations in the field of gold and silver HL prevail in design solutions. At the same time, the problem of silver leaching is considered in terms of the associated extraction of the main component. This approach is determined by a limited set of technological measures that have become an integral part of the classic technological regulation: ore crushing to the class –200–40 mm, sodium cyanide consumption at the level of 0,5 kg/t; pH value – 10,5; cycle duration 65 days or more; gold concentration in production solutions – fractions, mg/l; using activated carbon for sorption of noble metals. Processing ores with silver contents of 30 g/t and a more classical approach to gold HL does not allow to increase the degree of extraction. There is a need to modernize the circuit or change the parameters of the technological regulations. The object of the study was a sample of poor quartz ore provided by the customer developing one of the gold and silver deposits of the Far Eastern Federal District, the object was to increase the degree of leaching of silver from poor gold-bearing ores without changing the technological scheme and without attracting additional mining equipment. Critical analysis of literary data was carried out and the main directions of gold production from poor gold-bearing ores were identified. Chemical and mineralogical compositions of silver-containing minerals and ore rocks were investigated. Forms of association of silver with ore minerals and rocks have been established. The option of physical and chemical activation of increase of reactivity of cyanide solutions during heap leaching of silver from poor gold-bearing ores is chosen. In laboratory conditions, it was found that an increase in the concentration of sodium cyanide by 6 times or more contributes to a satisfactory extraction of gold both in agitation and percolation leaching of silver. However, in the latter case, the positive result was obtained only with the use of solutions with increased reactivity

Processing oxidized nickel ores (ONO) by shaft smelting is unprofitable. Introduction of hydrometallurgical methods will resolve this problem. In this work, according to X-ray phase (X-ray diffraction) and X-ray spectral microanalysis (XMA), the main sources of nickel and cobalt in the ONO are minerals of the serpentine group, primarily lizardite and antigorite. Heap leaching of nickel from ONO is studied and dependences are established for nickel extraction from acid solutions, acid consumption, and leaching duration. Parameters for leaching for the pause between irrigation, acid concentration, and the number of solution circulations at stages up to 10%, 20%, and ≥ 50% nickel extraction are proposed.

Uranium is the most basic material for the operation of nuclear power plants. Research on methods for extracting uranium efficiently and pollution-free is one of the hot issues in nuclear energy development. In nature, uranium is abundant in hard rock, but it is often wraped by volcanic rock. The traditional method of extracting uranium mainly uses heap leaching or in-situ leaching, but acid solution cannot enter the hard rock to extract uranium. In this paper, a highvoltage pulse power supply is designed with hydrogen thyristor as the switching device. The maximum output amplitude is 30 kV, the frequency is 1 Hz-1 kHz, and the pulse width is adjustable between 0-5μs. The influence of parameters such as the composition of uranium ore, the particle size of the ore, and the distance of the discharge electrode on the characteristics of the discharge electric field was simulated by COMSOL Multiphysics software, and the influence of the electric field intensity and its distribution relationship were obtained. Finally, the designed high-voltage pulsed power supply is applied to discharge the underwater volcanic rock. The results show that the discharge cannot significantly break the ore, but it can significantly reduce the mechanical strength of the ore and increase the porosity. The overall metal content in the composition of uranium ore determines the crushing effect mainly, and the electrode distance and particle size also affect the breakdown time and breakdown voltage. This method can also provide reference for other similar mineral processing.

A large-scale investigation into the effect of increased aeration on heap leaching of a pyrrhotite-rich pentlandite ore was commenced at the Terrafame mine in Finland. The typical reference air feed amount in operation is approximately 0.05 m3/metric ton/h, fed from one direction of the 330 to 350 m wide heap. In the current study approximately 62% higher air feed vs. reference operation was trialed by installing another layer of aeration from the opposite direction of the heap. The hypothesis was that air distribution across the ore would be improved and that the increase in air feed would result in faster oxidation of pyrrhotite, leading ultimately to improved recovery of valuable metals. The heaps were observed for 150 days after stacking. The results revealed an increase in the leaching rates of several metals: manganese, magnesium, iron, nickel and zinc leached 14, 171, 142, 1932, and 1309% more in the presence of extra aeration during the observation period. In addition, applying the extra air showed a 324% increase in the generation of acid within the heap.

Poor permeability, high mud and impurities contents, severe curing conditions and ore complexity are primary challenges faced by Yangla Copper Mine (YCM) during acid leaching, resulting in a poor 1% copper extraction after 3 months of traditional leaching. A series of technological improvements, which included of antiscalant addition, ore washing, classified crushing and screening, thin-layer conveying and dumping, and mechanical/chemical activation, were applied in YCM to enhance heap permeability and copper extraction from low-grade copper oxides. These improvements increased copper extraction to over 60 and the production of cathode copper reached 2500 t/a. Related topics such as: ore surface erosion, particle size distribution, heap structure, irrigation rate, and passivation and its effects are also discussed in this study. Even though some of the relevant mechanisms for enhanced recovery are still being studied, this successful industrial case provides a good reference for copper oxide mines encountering similar problems.

Sulfide-rich gold mill concentrates from the Cripple Creek & Victor Gold Mining Co. (CCV thus pelletizing CC&V mill concentrates is not likely to improve leach pad permeability or minimize acid generation. The combination of automated mineralogy, element mapping, and chemical analysis of leachates proved to be an effective means of monitoring leach behavior of fine-grained materials. The Ca element mapping was the most efficient method of monitoring cement binder degradation.

The present work relates to hydrometallurgy, in particular, to gold-bearing clay ores leaching processes. The initial and agglomerated material filterability was studied. Filterability varies in different agglomeration conditions. Influence of cement, lignosulfonate, plastizer (Cemmix CemPlast), lime consumption was investigated. The negative effect of organic reagents additives, such as plasticizer (Cemmix CemPlast) and lignosulfonate, on the filtration process was established. Colmatation of agglomerated ore minimizes at CaO and Ca (OH)2 using as a modifier of the system, also phase separation in the percolation regime and under pressure proceeds without difficulty. Lime and cement joint use in the optimum proportion at clay ore agglomeration under the studied conditions reduces the filtration duration from a few hours to 2-5 minutes.

It is well known that the Chilean mining industry is facing a shortage of water resources for the sustainable operation not only of existing plants but also of future projects. In addition, the depletion of oxide ores and those containing secondary sulfide copper will leave chalcopyrite ores as the main source of copper for future plants. To assure a sustainable hydrometallurgy plant, alternative water resources such as seawater and discard brine from desalination plants should be used together with a leaching process that can enhance the dissolution of chalcopyrite. This paper reports a study on the dissolution kinetics of finely ground copper oxide ore, chalcopyrite ore, and chalcopyrite concentrate leached in shake flasks, agitated reactors and columns using seawater and discard brine as the leaching solution. The type of chloride solution did not affect the dissolution of the copper oxide mineral. Regardless of the chloride solution used in the leaching test stirred at room temperature, the chalcopyrite dissolution did not exceed 4%, but increased to 90% when the temperature was increased to 50 °C. Column leaching of chalcopyrite ore with a P80 of 5 mm achieved a maximum dissolution of 43% of copper using discard brine at ambient temperature. The results show that curing time of the packed bed before the commencement of column irrigation and intermittent irrigation during leaching appeared to be important parameters to enhance dissolution of copper. Less irrigation time and more resting time can be beneficial for an industrial-scale heap leach plant.

Heap leaching is a well-known mineral processing technique, whereby crushed low grade ore is used for valuable metal extraction. The technique is typically used to extract precious and base metals, however, the metal extraction efficiency is relatively low. Even though reaction kinetics are extensively studied in heap leaching, the detailed hydrodynamic studies are still required to understand the underlying flow aspects. Heap hydrodynamics plays an important role in the transport of both leaching reagents and dissolved metal species and thus uniform liquid distribution through the ore mass is required. However, liquid channelling within the heaps has been identified as one of the main contributing factors for non-uniform liquid distribution. Since liquid channelling is supposed to be an inherent property in heap leaching systems, this work was primarily designed to explore the suitable techniques to improve liquid distribution and minimise liquid channelling in heaps. Intermittent liquid addition is employed and its effect on liquid channelling is studied, which has not been reported in the literature despite the application of it in industrial heaps. Both narrowly sized ore (16–20 cm) and realistic ore mixtures (2.36–25 cm) were studied in a pseudo 2-D Perspex column and the effect of rest period in intermittent leaching on liquid channelling was studied using out-flow liquid distribution measurements. The experimental results showed improved out-flow liquid distribution profiles and less channelling flow features in intermittent liquid addition conditions. The liquid out-flow profiles in both the packed bed systems were improved by resulting more flow paths through the particles and reduced features of liquid channelling. The narrowly sized fraction formed a near-Gaussian liquid distribution, which is the expected continuous probability based theoretical flow profile with drip emitter based liquid addition in heaps.

Due to decreasing ore grades and increasingly complex ore bodies, the heap leaching of sulfide ores is of increasing interest. In this research, the heap leaching phenomena of a pyrrhotite-rich pentlandite ore was investigated for the first 150 days of operation in order to understand the phenomena taking place in the early phase of leaching in an industrial scale heap. The ore investigated originates from Terrafame (Finland) and contains approximately 20 wt% metal sulfides, the majority of which are pyrrhotite and pyrite. The nickel and zinc minerals of interest, pentlandite and sphalerite, are minor constituents of the ore. The oxidative leaching behavior of sulfidic minerals was shown to follow for the most part the order of nobility of sulfides. In the heap leaching investigated, pyrrhotite especially was shown to be far more reactive than pentlandite and sphalerite and thus the recovery of valuable metals can occur only after pyrrhotite dissolution. It was found that the nickel, zinc, and copper present in the irrigation solution can partially precipitate into the heap where more reductive metal sulfides, such as pyrrhotite and alabandite, are present, a metathesis phenomenon postulated elsewhere for copper and now confirmed in industrial scale operation. Pyrrhotite was also shown to create the majority of the reagent (acid and oxygen) demand and the majority of the reagent demand variation during the early days of heap leaching. In addition, the height of the heap was shown have an important role in determining the leaching time, due to physical, chemical, and practical limitations on acid feed. The acid demand for pyrrhotite leaching in low-oxygen consuming reactions was found to be higher (approx. 62 kg/tonne of ore) than the possibility to feed acid on a tall heap (23 kg/tonne of ore at maximum). This was shown to result in heavy precipitation of iron compounds, such as goethite. The results give more clarity for the initial stages of leaching at Terrafame and thereby enable clearer strategies to be formulated for solution circulation management according to heap age.

Several mechanisms contribute to changes in the performance of oxide copper heaps. These include physical, biological, chemical and thermal interactions between sulfuric acid and the formation of soil particles. A series of experimental studies was conducted by simulating the column leaching process in the laboratory. The leaching of selected gravel and crushed copper oxide ores from two copper mines was carried out to measure their permeability and strength. The influence of effective parameters on gravel clogging was studied and the clogging coefficient was estimated with time. Furthermore, the ratio of particle reduction (RPR) caused by acid seepage was evaluated and an equation for the internal friction angle of ore particles over time was generated. The present study shows significant reductions of gravel permeability (28% after five months leaching) and friction angle of ore particles (25% after eight months leaching). The effects of sulfuric acid flow on the hydro-mechanical properties of oxide copper heap soils could enhance the accuracy of slope stability design and drainage layers design in industrial heap leaching systems.

Heap leaching is being increasingly explored as a lower cost metallurgical technology to extract copper from sulfide ores of low grade and quality. Heap temperature is a critical factor in achieving economic copper extraction. The determination and control of heap temperature is challenging due to the intrinsic complexity of the intertwined fundamental processes occurring simultaneously inside a heap. In this study, we applied the HeapSim-2D model, calibrated using data provided by the Quebrada Blanca Mine, to study the response of heap temperature to variations of four key design parameters: raffinate flow rate, raffinate temperature, the extent of pyrite oxidation, and the application of a thermal cover. Note that the reported results have not been validated against experimental data and other possible rate-limiting factors are presently ignored. The modelling results showed that at a fixed raffinate temperature, the average heap temperature approached the raffinate temperature faster at a high flow rate than at a low flow rate. The heat generated by the oxidation of pyrite led to an increase in the heap temperature, but the magnitude of the increase was negligible at high raffinate flow rates, which would remove the generated heat via convection by the bulk movement of the leaching solution. The model predicted that the application of a thermal cover had a positive effect on maintaining the heap temperature, but the effect also depended on the raffinate flow rate. Understanding the effects of these design parameters on heap temperature is critical for achieving optimum copper extraction in heap leaching.

Leaching and micro-focus X-Ray computed tomography (µXCT) characterization studies were performed on a synthetic silver ore prepared from cement mixtures with embedded silver grains. This was done with the aim to understand the leaching behaviour of coarse ore particles in laboratory-scale heap leaching experiments. The synthetic ore was developed to possess specific ideal properties including uniform grain dispersion and size, homogenous porosity, and even grade distribution, and the “homogenized ore” was evaluated for these characteristics. The study validated that the ore had achieved its homogenized properties; however, the inner-particle pores were not found to be continuous at the µXCT detection limit of 4.8 µm. Poor extraction from the coarse particles in the leaching investigation suggested the pore network was not well established and may exist only at the sub-micron scale. Coarse particle leaching extraction data was analysed with the diagnostic shrinking core and the extended mixed topology models, which demonstrated that a diffusion–reaction mechanism governed the dissolution extraction from the larger particles. The results showed that leaching was restricted to the near-surface regions, but did not extend to the inner core, resulting in low extraction. Coarse synthetic particle leaching under controlled conditions could be utilized as a potential deterministic technique for understanding the reaction performance in coarse particle heap leaching.

In this study, Ore granite samples were collected from Gattar site for leashing of yellow cake. The process involves heap leaching of uranium through four main steps; size reduction, leaching, uranium purification and finally precipitation and filtration. The separation process has been given in details and as flow chart. Gamma spectrometry based on HpGe detector and energy dispersive X-ray (EDX) were used to assay uranium content and activity before and after separation. The uranium weight percentage value as measured by EDX were found to be 40.5 and 67.5% before and after purification respectively. The results of the calculations based on gamma measurements show high uranium activity and that the uranium activity ratios values are 0.045 ±4.9%, 0.043 ±4.7% and 0.046 ±2.3%, before purification. While these values were found to be 0.050 ±3.3%, 0.049 ±3.3% and 0.050 ±2.7%, after purification, respectively. The results are discussed in details in the paper.

This study explored the processing of chalcopyrite ore through heap leaching followed by flotation. Crushed and agglomerated chalcopyrite ore was subjected to bacterially-assisted leaching at ambient temperature in columns that ranged in height from 1 m to 5 m. > 50% extraction was obtained after 16 months. Chalcopyrite leaching was affected only by time, not irrigation rate, acid delivery rate, or column height. This indicated that chalcopyrite heap leaching was reaction-limited rather than transport-limited, and therefore relatively impervious to scale. The findings suggest that chalcopyrite could be leached in substantially taller heaps, releasing proportionally greater quantities of copper, without sacrificing recovery. Leaching of the chalcopyrite ore had little effect on its floatability, as indicated by rougher flotation testing. The maximum flotation recoveries, RMAX, were 90% and 88% for the ore and leached residues, respectively. The combined leach/float recoveries were greater than the individual copper recoveries from leaching and flotation alone. This was simply due to the initial leaching step recovering some of the copper that would have been inevitably lost to flotation tailings. Such a leach/float approach may actually benefit from the low reactivity of chalcopyrite, which ensures that leaching would never be so extensive as to affect the later floatability of the mineral.

For some years it has been suggested that microwave treatment (MT) of ores might result in preferential grain boundary fracture that would have potential benefits during downstream recovery processes. These benefits include energy savings during subsequent comminution due to particle weakening and improved exposure or liberation of value grains. This suggests that heap leaching could benefit from microwave-induced grain boundary fracture, as the extent and kinetics of heap leaching processes depend on the accessibility of grains to lixiviants. The aim of this study was to determine if microwave treatment (microwave exposure time of 1 s and specific energy inputs of between 2 and 3 kWh/t) of small (5 + 4.75 mm), medium (16 + 9.5 mm), and large (25 + 19 mm) crushed sphalerite ore particles prior to heap leaching would result in improved metal extraction. Column bioleaching experiments showed improved metal recoveries (over 23% to 26%) for microwave treated particles of all sizes. Analysis of the particles by X-ray computed tomography and image analysis techniques showed increased internal cracking due to microwave treatment. This was correlated with the increased recovery during heap bioleaching.

The Sawayardun Gold Mine, the first Muruntau type gold mine in China, was located in the south Tianshan Mountain, Xinjiang Province. The gold reserve was 127 t with an average gold grade of 2.36 g/t. Due to the high content of arsenic and antimony, the traditional flotation-roasting-cyanidation process was not suitable. The direct cyanidation gold extraction for the raw ore was 44.70 %. Thus, biooxidation experiments in shaker flasks were conducted for this ore. The optimum conditions were obtained as inoculation volume 10 %, initial pH 1.7, pulp density 15 %, temperature 33 °C, leaching time 10 days, with the arsenic oxidation rate of 75.12 %. Then the biooxidation residues were test for gold leaching using NaCN, green gold leaching agent and thiourea. After 24 h leaching rate at pulp density of 33%, gold leaching agent dosage of 2 kg/t ore, the gold extraction for NaCN, green gold leaching agent and thiourea were 91.50 %, 86.23 % and 91.09 %, respectively. The high gold extraction showed a bright future for the whole-ore heap biooxidation of this refractory gold ore.

Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.

Heap biooxidation is the most economic option of treating processing plants tailings and refractory ores containing non-ferrous and precious metals and sulphides.Pyrite tailings of copper ore processing (Sample 1), tailings of sulphide copper-nickel ore processing (Sample 2) and double refractory gold-bearing ore (Sample 3) were studied.Autotrophic microorganisms Acidithiobacillusthiooxidans and Acidithiobacillusferrooxidans were used for the tests. The duration of heap biooxidation tests for Samples 1, 2 and 3 was 6, 10 and 16 months, respectively. The rates of copper and zinc recovery into solution during heap biooxidation of Sample 1 were 68% and 71%, respectively; the rates of copper and nickel recovery from Sample 2 were 50% and 75%, respectively. Base metals were extracted from solution to selective high-grade concentrates after biooxidation.Biooxidation tailings of Samples 1 and 3 were leached using an alkaline sodium cyanide solution. The recovery of gold from Sample 1 and Sample 2 was 65% and 85%, respectively.

JOGMEC has been carrying out the study on primary copper sulfide ores leaching for recovering copper economically and efficiently by heap leaching. In our study, we have been using the primary copper sulfide ore produced in an IOCG deposit. The ore is characterized by high iron content and high acid consumption in leaching. For the optimization of the leaching, the conditions such as ore size, agglomeration, pH and irrigation rate of leaching solution were examined with column leach tests. The best result was over 80 % extraction of copper in 150 days with leaching solution of 1 M sulfuric acid and temperature of 45 °C. In this experiment, the fines of the ore sample were removed before putting it into the column to keep the permeability of the ore bed. In these column leach tests, the Fe2+/total-Fe ratio of PLS decreased gradually by the activity of naturally grown iron-oxidizing bacteria. The bacteria in PLS, which have the ability of iron-oxidizing and sulfur-oxidizing, were identified by next-generation sequencing as Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. We also carried out bench-scale tests with about 200 tons of the primary copper sulfide ores. Iron-oxidizing and sulfur-oxidizing bacteria were identified in the leaching solution as same with column leach tests. It is considered that the bacteria worked in the leaching solution and on the surface of the ores.