Dump Leaching Research Articles

Increasing the Duration of Dump Leaching of Copper Under Winter Conditions

Increasing the Duration of Dump Leaching of Copper Under Winter Conditions

A review of the influence of blast fragmentation on downstream processing of metal ores

Rock fragmentation is one of the most commonly optimized blasting outcomes due to its significant influence on the efficiency of downstream operations. This paper reviews the influence of blast fragmentation on processing of metal ores. Two aspects of rock fragmentation that influence downstream mineral processing operations include the particle size of the run-of-mine ore and the degree of internal microfracturing in the fragments induced by blasting. The main influences identified include productivity of comminution equipment, energy consumption in comminution equipment and mineral recovery. An increase in blasting energy results in higher throughput and energy reduction in comminution circuits. Increase in blasting energy results in energy savings in the overall mining operations. However, when increasing the blasting energy, the environmental and safety impacts must be taken into consideration. Blast-induced microfractures increase the permeability of the fragments, therefore enhancing mineral exposure to leaching reagents and consequently may lead to higher mineral recoveries, particularly in heap and dump leaching operations which employ-one-stage comminution. However, the textural characteristics of the ore also influence the mineral recovery. Further research should focus on establishing the relationship between blast intensity and mineral leaching recovery for metal ores of different textural properties.

Studies on uranium recovery from a U-bearing Radoniów Dump

Abstract This work reports the possibility of uranium recovery from a post-mining uranium ore dump in Poland by a bioleaching method. The studies were conducted on the dump leaching model with the mass of 570 kg of uranium bearing mineral material from Radoniów pile and in the periodic bioreactor with a work volume of 80 dm3 and with mechanical mixing and aeration of the charge. The uranium concentration in the examined material was about 800 ppm. In this process, the consortium of microorganisms isolated from former mines was used. It was composed of the following microorganisms: Bacillius, Pseudomonas, Sphingomonas, Thiobacillus, Halothiobacillus, Thiomonas, and Geothrix. The efficiency of the uranium bioleaching process was 98% in the reactor, and a yield of 70% was obtained in the dump leaching model. The post-leaching solution contained significant amounts of uranium ions that were separated in two stages: (1) by ion chromatography and then (2) by a two-step precipitation method. The resulting solution was a source of ammonium diuranate, the precursor of yellowcake (uranium oxides).

How copper dump leaching works

In copper dump leaching, run-of-mine ore is irrigated with acidic leaching solution to generate aqueous cupric ions for further processing. The very large size of the ore particles being leached, as much as two meters in diameter, should preclude any significant metal recovery. Dump leaching should not work; and yet it does. This study investigated the leaching of coarse-sized copper sulphide ore, with top sizes ranging from 150 to 250 mm. The simulated run-of-mine ore sizes were leached for more than six months. The data collected from these experiments included particle size distributions before and after leaching, copper distributions by size before and after leaching, and leaching kinetics at various irrigation rates. The results showed that leaching causes particle breakage. That breakage results in a continuous generation of fines and a continuous supply of fresh mineral surfaces for leaching. Dump leaching can be explained by a mechanism of breakage and fines generation. The rate of copper leaching in dumps is a product of the rate of fines generation and the rate of leaching of the fines.

Recent progress in biohydrometallurgy and microbial characterisation

Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and the biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisation.

Unravelling the Complexity of Heap Bioleaching

Heap and dump leaching of sulphide minerals have become well-established techniques for the processing of low grade ores, especially of copper, over the past 30 years. The oxidative dissolution of sulphides in heaps can be significantly enhanced by microbial colonies, but the complexities of the heap leach process overall often counteract the potential advantages, or prevent microbial colonisation and bioleaching in the first place. This overview discusses the multiple layers of complexities that govern percolation leaching processes, such as the interactions between mineral grains, particle pores and leach solution, microbial responses to solution chemistry typical of heaps, solution and solute transport in heterogeneous unsaturated ore beds, as well as heap aeration and microbial response to CO2 supply. It becomes clear that economically successful heap bioleaching hinges on careful engineering and operation of the heap process as a whole to create an environment in which microbial colonies can thrive and the value metal is released sufficiently rapidly into solution.

Application of aerial image analysis for assessing particle size segregation in dump leaching

Understanding the behaviour of fluid flow through packed ore/rock beds is essential for estimating metal extraction from low-grade ores via dump leaching as well as the release of toxic elements from mine waste rocks. One fundamental factor that determines the flow behaviour in ore/rock beds is particle size distribution. Given the limitations presented by the traditional sieve analysis, we applied aerial imagery to investigate the particle size distribution in ore piles. Using dump leaching as an example, we analyzed the aerial images of a dump leach pad acquired by a camera installed on a drone while the leach pad was under construction. The image analysis results showed that the dump leach pad contained an extremely wide range of particle sizes. A spatial segregation of fine and coarse particles was observed. The widely used P80 was deemed to be questionable to represent particle size distribution in dump leach pads. The Sauter mean diameter (d32) and the dump permeability were found to increase with depth. The technical method described in this study provides a more convenient and reliable tool for particle size distribution analysis, thereby facilitating future studies that will enhance understanding of metal extraction from low grade ores in leaching operations as well as the potential release of pollutants from waste rock piles.

Predicting Future Water-Quality Impacts from Mining: A 52-Year-Old Field Analog for Humidity Cell Testing, Copperwood Deposit, Michigan

Modern mine development requires consideration of environmental management, including long-term, post-closure conditions. A pile of ore from test mining of the Copperwood deposit in 1957 subsequently weathered under ambient local conditions for 52 years prior to this study. This study used the ore pile as a long-term field analog to evaluate conceptual models for scaling of bench-scale humidity cell tests commonly used to assess the potential for mine wastes to generate acidic and/or metalliferous drainage waters. The Copperwood ore is simple, with only one sulfide mineral (chalcocite) hosted by gray to black shale. As part of the new Copperwood development work, a drainage system was established beneath the ore rock pile to collect water that had infiltrated through and weathered the ore material. The composition of the drainage waters today, after approximately 52 years of weathering, can be used to test conceptual predictive models of water-rock interaction. Using inferred “steady-state” rates of release from a 40-week humidity cell test and a simple conceptual model of weathering, the predicted release of elements from the ore rocks was greater than the actual composition of present-day drainage waters. This discrepancy is interpreted to indicate that the steady-state release rates inferred by the humidity cell test are not actually steady state but are the initial stages of a long-term progressive decline. As a result, use of the humidity cell test without calibration to field conditions would significantly overestimate the potential for mine rocks to affect water quality. While progressive decline of release rates has been documented in some multiple-year laboratory testing and heap and dump leaching, it is not yet possible to estimate the ranges in rates of decline as a function of waste mineralogy, fragment size, and other factors, because sufficient long-term studies such as the one presented here are lacking. This case study shows how a variety of methods can be applied to help properly calibrate humidity cell testing to field conditions, so that mining projects can reliably predict the chemistry of waters draining mined products decades into the future.

Recovery of copper sulphides mineral grains at coarse rock fragments size

Assuming the random distribution of sulphide mineral grains and random rock breakage, a relatively small percentage of sulphide grains will be exposed on the rock surface. Early liberation of sulphide grains needs to be considered in terms of the mechanical properties of such grains relative to the properties of the host rock matrix.Clustering of sulphide mineral grains, will make early liberation possible. Depending on the nature of mineral associations, crushing of such rocks will result in different outcomes. Where clustering is manly of very soft copper minerals, with the host rock being moderately strong feldspars or quartzite’s, the copper rich parts of rock are likely to fragment first, resulting in relatively small size being rich in copper minerals. However, in the case of moderately strong chalcopyrite, the difference in elastic properties between chalcopyrite and feldspar or quartz, will not be significant enough to cause a propensity for early liberation.Where clustering of copper minerals occurs with grains of pyrite (or magnetite), the stronger part of the rock fragment will be one rich in valuable minerals. During crushing of such rock, the sulphides rich zones will fragment in a different way than gangue. Stress concentration within pyrite (or magnetite) will result in failure of the relatively soft surrounding matrix, thus promoting liberation of chalcopyrite or chalcocite grains. Therefore, textural information about the associations of sulphide minerals (copper sulphides vs. pyrite/magnetite/garnet) will be of critical significance in the evaluation of the propensity for coarse liberation of copper sulphide minerals. An absence of close spatial associations will significantly reduce the possibility of early liberation of copper sulphides.During blasting ore is exposed to sufficiently intense, high-strain rate loading to be able to induce micro-fracturing originating from individual sulphides mineral grains as well as their clusters. Due to the high rate of loading, a substantial amount of energy can be dissipated with embryonic rock fragment, before macro-failure of rock, which will relieve rock of blast induced stress. Created micro-cracks will play a significant role in subsequent comminution, where rock fragments with enhanced density of micro-cracks will be crushed more easily. Extensive micro-cracking is also likely to play a significant role during heap or dump leaching, stimulating infiltration/diffusion of leaching fluids into the interiors of rock fragments.

Biomining: an Established and Dynamic Biotechnology

“Biomining” is generic term to describe the application of living organisms to extract and recover metals from mineral ores and waste materials. Since its inception as a crude technology (“dump leaching”) for treating “run of mine” rocks and boulders that contained too little copper to be processed by conventional processing, engineering options used in biomining have become increasingly refined and diverse. Currently, microbiological processing is used to extract both base metals (copper, and to lesser extents nickel and zinc) and precious metals (mostly gold) from ores and mineral concentrates in heaps and stirred-tank bioreactors, as well as in dumps. Recent developments include the demonstration, at pilot-scale, of indrect leaching of zinc sulfide concentrates, in which the biological step (regeneration of ferric iron) is carried out independently of abiotic mineral oxidation, and using microbiologically-mediated reductive dissolution of ferric iron minerals to liberate nickel from lateritic ores.

Research on Reinforcing Acid Leaching of a Refractory Copper Oxide Ore with High Content of Slime and Iron Minerals

The characteristics of Yangla copper oxide ore and acid leaching of this copper ore were investigated. The results indicate direct dump acid leaching of raw ore is not feasible for the treatment of this copper ore in practice. Sieve sizing-warming-stirring-acid leaching process was employed for the treatment of the fine grain materials below 1m, while 66.19% copper leaching efficiency and10.92 t H2SO4 consumption for per ton are obtained. Dump acid leaching process was employed for the treatment of the coarse grain materials above 1 mm, while 68.65% copper leaching efficiency and 15.43 t H2SO4 consumption for per ton copper are obtained. Key techniques are that sieve sizing process strictly controls the content of fine grain materials in dump leaching process and the searches ability of H2SO4 for the internal copper ore is improved, while warming-stirring-acid leaching process reinforces the copper leaching efficiency of fine grain materials. The proposed in this paper will be of benefit to the utilization of similar refractory copper oxide ore with high content of slime and iron minerals.

Weathering of Biotite in Acidithiobacillus ferrooxidans Cultures

The purpose of this study was to assess the weathering of biotite under conditions simulating an active bioleaching environment. Finely ground biotite was contacted with Acidithiobacillus ferrooxidans culture solutions for up to 120 days. Biotite was altered under these conditions to interstratified structures comprised of mixed layers of biotite and vermiculite. Interlayer K in biotite was released upon weathering and precipitated with ferric iron and sulfate to form jarosite. Substantial dissolution of biotite was also associated with weathering. The data demonstrate that exposed, biotite-rich rocks in mine tailings and heap and dump leaching systems can undergo acid mediated solubilization and structural changes, which are coupled with the formation of expansive, vermiculite-like minerals and jarosite precipitation.

Experimental study on preferential solution flow during dump leaching of low-grade ores

The phenomenon of preferential solution flow during dump leaching of low-grade ores was studied. The formative mechanism of preferential solution flow was investigated through analyzing the relationship between permeability and ore diameter, and the relationship between surface tension and ore diameter. The preferential solution flow happened within the fine ore area when the dump was unsaturated. And it could happen within the coarse ore area when the dump became saturated. The results of experiment show that the outflow of coarse ore area increases sharply with higher applied rate. The outflow of fine ore area is greater than that of coarse ore area when the applied rate is below 3.2 L/min, and the preferential solution flow happens in fine ore area. But the preferential solution flow happens in coarse ore area when the applied rate is higher than 3.2 L/min. The result of the experiment is consistent with the mechanism analyzing.

Study on preferential flow in dump leaching of low-grade ores

Preferential flow in dump leaching of low-grade ores was investigated in this paper. The production of the dump leaching plant at Dexing Copper Mining in China was significantly influenced by preferential flow due to the heterogeneity of the ores in dump. Surface tension, negative pore water pressure, matrix suction and permeability of dump were found to be correlated to particle size. Preferential flow, which occurred in the fine and coarse region, was determined by solution application rate. Experiments showed that preferential flow happened in the fine region at an application rate below 1070 L/m 2 min. Experiment of solute transportation under preferential flow was conducted by selecting NaCl as solute. The NaCl concentration of the outflow from the coarse region was greater than that of the fine region. The leaching rate increased slowly as the leaching process proceeded because NaCl dissolved in the immobile water could only be leached through diffusion. The percentage recovery of coarse region surpassed 100%. The preferential flow within the fine region under the condition of small application rate was confirmed.

Experimental Study of Preferential Solute Transportation During Dump Leaching

Abstract The production of dump leaching of the Dexing Copper Mine was affected by a preferential solution flow. Formative mechanism of the preferential solution flow was investigated by analyzing the relationship between both dump permeability and surface tension and ore diameter. The preferential solution flow occured in the fine ore area when the application rate was low. The preferential solution flow entered into the coarse ore area because the negative pore water pressure disappeared with an increase of the application rate. The preferential solute transportation experiment was conducted by selecting NaCl as mineral. Results of the experiment showed that the concentration of the outflow solution reduced over time. The concentration of the coarse ore area outflow solution was greater than that of the fine ore area. The process of NaCl leaching can be divided into two stages. NaCl was carried out directly by diffusion - convection during the first stage, so the leaching rate increased sharply. But in the second stage, only a small amount of NaCl dissolved in the immobile water. The leaching rate increased slowly because NaCl, dissolved in the immobile water, can only be leached by diffusion.

Formative mechanism of preferential solution flow during dump leaching

Preferential flow is a rapid movement of solution through pores caused by coarse ores. Macropore is the main factor for the preferential flow. Macropore can be defined from three aspects. Segregation of the ores during dumping was studied according to particle kinematics. Small ores become smaller under the effect of acid and weathering. Clay in the rainwater from the hillside precipitates in the dump. Segregation and fine ores are the main causes in macropore. The permeability in coarse ores is better than that in fine ores. The mechanism in the preferential flows was studied combining the fast conducting effect of the macropore. Experimental result shows that, at certain application rate, fine ore area is saturated while large volume of solution flows laterally to the coarse ore area and leaks out quickly through the macropores. Thus the mechanism of preferential solution flows is further illustrated.

English

There are many mature Cu heap leach facilities in the western United States that will face closure in the next decade. However, there is little published information on the response of groundwater systems to the cessation of leaching. Copper dump leaching was conducted on the Bingham Canyon Eastside waste rock dumps between 1963 and 2000. Leach water discharging from the toe of the waste rock dumps had a typical pH of 2.9 and a total dissolved solids concentration of about 90,000 mg/L. During active leaching this water was recirculated, but now it is neutralized as it enters the mine's tailings and process water circuit. With the end of leach water application, average annual flows discharging from the toe of the dumps have declined rapidly from 1500 L/s in 1998 to approximately 45 L/s in 2004. Average acidity in water discharging from the toe of the dumps declined by almost thirty percent between 2000 and 2005, and since 2003, most solute concentrations have declined by about ten percent. The only exception is Cu concentration which has increased by a factor of four since 2000. Water quality in the underlying saturated bedrock has also begun to improve. Since 2000, sulfate concentrations have declined by a third, alkalinity has increased, and Cu and Zn concentrations have declined by up to ninety percent in water from tunnels that receive at least a portion of their inflows from beneath the waste rock footprint. Water quality in bedrock and alluvium down gradient of the dump toe began to improve after the leach water collection system was upgraded between 1994 and 1996. Arithmetic mean sulfate concentrations in down gradient alluvial monitoring wells declined from a high of 6000 mg/L in 1994 to less than 1000 mg/L in early 2004. These data illustrate how the groundwater system responds to the termination of waste rock and heap leach operations and may provide a useful analogue for the closure of other Cu heap leach operations.

Rule of oxygen transmission in dump leaching

According to the chemical equations, the flux and concentration of oxygen required during bacterial leaching sulfuric mineral were investigated; the rule of air bubble transmitted in granular was researched in the Dump Leaching Plant of Dexing Copper Mine. The results show that lack of oxygen in dump leaching is the critical factor of restricting leaching reaction. Pyrite is the primary oxygen-consuming mineral in bioleaching. When its content is too high, it needs a great deal of oxygen for reaction and competes for the finite oxygen with objective minerals, and thus the leaching velocity decreases greatly. The average size of ore particles and diameter of bubbles are the key parameters affecting the mass transfer coefficient. Reverse analysis was adopted, and it shows that 44.8 m3 air per unit ore can meet the requirement of production if the molar ratio of pyrite to chalcopyrite is 10.

Improvement of the quartz sand processing at Hohenbocka

The raw sands from Hohenbocka (Germany) containing iron essentially in pyrite form is used for glass grade sands processing by dump leaching for several weeks followed by attrition and two-stage classification. The analysis of the sands by means of X-Ray Fluorescence Analysis (RFA) showed an average of about 420 ppm Fe. The objective of this investigation was to reduce the processing time and the total iron content below 105 ppm in the sand product for special glass applications. Due to the presence of sulfide and oxide iron at different ratios in raw sands, a combination of chemical and physical methods was investigated. Leaching was carried out at different acid concentrations, followed by surface cleaning by neutral and alkaline attrition, and gravity separation. Additionally, the effect of continuous addition of H 2O 2 during leaching to remove iron from sands was investigated. Only two days of leaching was required at the initial acid concentration to 25 g/L. After attrition and tabling of leached sands, a product with 84 ppm of iron was achieved. The continuous removal of dissolved metals by adsorption with active carbon could make it possible to reuse the regenerated sulphuric acid for leaching. With recirculation, the quantity of fresh sulphuric acid required was 0.4 kg/t of quartz sand.

Present and future commercial applications of biohydrometallurgy

Modern commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching at the Kennecott Copper Bingham Mine. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for bioheap copper leaching of higher-grade, higher value ores. This commercial practice is exemplified by at least 11 mining operations. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps. Now, bioleaching has been extended to the commercial extraction and recovery of cobalt. Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near-term future commercial applications will likely remain focused on recoveries of copper, gold and possibly nickel. Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactors. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component.