Influence of jarosite precipitation on iron balance in heap bioleaching at Monywa copper mine

Ferric iron is an important oxidant in sulfide ore bioleaching. However, recirculating leach liquors leads to excess iron accumulation, which interferes with leaching kinetics and downstream metal recovery. We developed a method for controlling iron precipitation as jarosite to reduce excess iron in heap bioleaching at Monywa copper mine. Jarosite precipitation was first simulated and then confirmed using batch column tests. From the simulations, the minimum pH values for precipitation of potassium jarosite, hydronium jarosite, and natrojarosite at 25 °C are 1.4, 1.6, and 2.7, respectively; the minimum concentrations of potassium, sulfate, ferric, and sodium ions are 1 mM, 0.54, 1.1, and 3.2 M, respectively, at 25 °C and pH 1.23. Column tests indicate that potassium jarosite precipitation is preferential over natrojarosite. Moreover, decreased acidity (from 12 to 8 g/L), increased temperature (from 30 to 60 °C), and increased potassium ion concentration (from 0 to 5 g/L) increase jarosite precipitation efficiency by 10, 5, and 6 times, respectively. Jarosite precipitation is optimized by increasing the irrigating solution pH to 1.6. This approach is expected to reduce the operating cost of heap bioleaching by minimizing the chemicals needed for neutralization, avoiding the need for tailing pond construction, and increasing copper recovery

Study on the second stage of chalcocite leaching in column with redox potential control and its implications

High-grade natural chalcocite (Cu2S) was leached in column under controlled redox potential (Eh). To satisfy the requirements of the shrinking core model, the conditions in the column were kept as uniform as possible by adopting a short height of the middle chalcocite layer, high acid Fe-2(SO4)(3) feed and high irrigation rate. The effects of temperature, Fe3+ concentration and Eh on the second stage of chalcocite leaching were investigated. The second stage is sensitive to temperature whereas insensitive to the variations in Eh and Fe3+ concentration above a certain level. The second stage was divided into two &quot;sub-stages&quot; based on the inflection point at approximately 70% copper dissolution. The excellent linear relationship plotted by the mixed-kinetics indicated that the second stage is controlled by the rates of both chemical reaction and diffusion, in which the limitation of the chemical reaction rate is dominant. The second &quot;sub-stage&quot; (&gt;70% dissolution) is responsible for the slow kinetics of the second stage. Mineralogical study of the residues confirmed that a S-0 product layer covered around a shrinking CuS core during the second stage. In addition, high temperature resulted in a more porous S-0 layer which remarkably influences the ion diffusion rate. A dissolution model based on the shrinking core model was proposed. Implications of the findings for heap bioleaching were discussed. (C) 2015 Elsevier B.V. All rights reserved.</p

Activation of Dolomite Flotation by Ferrous Hydroxide and Carbonate

The major problem with Carlin-type gold deposit flotation is that the high dolomite content in the concentrate decreases the quality of gold. Further, the activation mechanisms involved in dolomite flotation are still not fully understood. Herein, the correlation of Fe2+ conversion with xanthate adsorption and dolomite flotation was investigated to reveal the effect of dolomite embedded with pyrite. Flotation tests suggested that Fe2+ rather than Fe3+ improved the floatability of dolomite from 20% to 45%. Contact angles and thermodynamic tests indicated that the hydrophobicity of Fe2+-modified dolomite corresponds to the adsorption of xanthate. Importantly, time-of-flight secondary ion mass spectroscopy (Tof-SIMS) and x-ray photoelectron spectroscopy (XPS) attributed the activation of dolomite flotation to the formation of Fe(OH)2 and FeCO3. The coordination model of flotation successfully elucidated the selective adsorption of xanthate between Fe(OH)2, FeCO3 and FeOOH surfaces. The density function theory (DFT) simulation calculation was performed to identify the reaction rate at the atomic level, and the density of states (DOS) was also conducted to verify the conclusions at the electronic level. This study presents important surface chemistry evidence for understanding and regulating the poor selectivity in the flotation of Carlin-type gold deposits

Investigation on the correlation between ferrous ion and the floatability of pyrite with different oxidation degrees

This work aims to establish the quantitative relationship between the surface oxidation state of pyrite and flotation performance. In this paper, an efficient method was proposed to prepare pyrite with different oxidation degrees. Flotation tests show that the floatability of pyrite decreased with prolonging the oxidation time. TofSIMS results reveal that the main component on the oxidized pyrite surface is Fe hydroxides or oxides. XPS analysis confirms that Fe(OH)2 and FeOOH are the main formula of Fe species, and the ratio of Fe2+/Total Fe agrees well with the floatability of pyrite with different oxidation degrees, which can be taken as an index to develop the flotation performance of pyrite. DFT simulation calculation further demonstrates the reliability of Fe (OH)2 as the active site. This study provides essential surface chemistry evidence for correlating the surface species with the floatability of pyrite with different oxidation states through quantitative analysis of various intermediate products

Contributions of Microbial "Contact Leaching" to Pyrite Oxidation under Different Controlled Redox Potentials

The function of microbial contact leaching to pyrite oxidation was investigated by analyzing the differences of residue morphologies, leaching rates, surface products, and microbial consortia under different conditions in this study. This was achieved by novel equipment that can control the redox potential of the solution and isolate pyrite from microbial contact oxidation. The morphology of residues showed that the corrosions were a little bit severer in the presence of attached microbes under 750 mV and 850 mV (vs. SHE). At 650 mV, the oxidation of pyrite was undetectable even in the presence of attached microbes. The pyrite dissolution rate was higher with attached microbes than that without attached microbes at 750 mV and 850 mV. The elemental sulfur on the surface of pyrite residues with sessile microorganisms was much less than that without attached microbes at 750 mV and 850 mV, showing that sessile acidophiles may accelerate pyrite leaching by reducing the elemental sulfur inhibition. Many more sulfur-oxidizers were found in the sessile microbial consortium which also supported the idea. The results suggest that the microbial "contact leaching" to pyrite oxidation is limited and relies on the elimination of elemental sulfur passivation by attached sulfur-oxidizing microbes rather than the contact oxidation by EPS-Fe

A nanoscale qualitative study on the role of sodium hydrosulfide in oxidized carrollite flotation

The surface species transformation of oxidized carrollite processing with NaHS and KBX was investigated. Flotation and contact angle tests indicate that the combination of NaHS and KBX takes a better flotation performance than adding NaHS or KBX alone. Thermodynamic analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) results confirm the stronger chemisorption of KBX occurs on the oxidized carrollite surface with NaHS, which is beneficial to remove the cobalt oxides, thus contributing to the superior floatability. Interestingly, less elemental sulfur was observed on the carrollite surface as the interaction of NaHS and KBX than adding NaHS alone. It suggests that elemental sulfur is not the main contributor to the restored floatability of oxidized carrollite through sulfidisation. This study provided a new perspective to correlate the surface species with xanthate adsorption and oxidized carrollite flotation through determining the various intermediate products. (C) 2021 Published by Elsevier B.V. on behalf of China University of Mining & Technology

Characterization of microbial community in industrial bioleaching heap of copper sulfide ore at Monywa mine, Myanmar

Microbial communities and activities in multi-lift bioleaching heap of copper sulfide ore were investigated at Monywa copper mine, Myanmar. The high-throughput sequencing method revealed a microbial community dominated by archaeal Ferroplasma (about 70%), rather than more commonly reported genera of Acidithiobacillus and Leptospirillum (together about 25% in Monywa heap). Multi-lift stacking operation without heap aeration resulted in low oxygen concentrations in the heaps (leachate oxygen concentration of 0.35 mg L-1 to 0.68 mg L-1). Therefore, low oxygen concentrations, high organic matter concentrations and moderate temperature in the heaps favored the growth of versatile Ferroplasma which can both undergo autotrophic and heterotrophic growth. Total cell number in the irrigation solution and leachate was in the range of 4.86-8.80 x 106 mL(-1), and the detected microbes in ore residues and leaching solutions were mainly those with iron-oxidizing ability. Their iron-oxidizing rate showed highest at the temperature of 35 degrees C, while in heaps may be limited by the low oxygen supply. Monywa bioleaching system with the above mentioned microbial community and activity formed a leaching solution of low redox potential, resulting in appropriate pyrite oxidation during chalcocite dissolution, thus helped maintain relatively stable acid and iron concentration in the cycling leaching solution. This study explained the formation of the microbial community and activity in Monywa heap leaching, linking to its heap physical and chemical conditions, and suggested that the role of Ferroplasma in bioleaching system may have been overlooked previously, especially in oxygen-limited bioleaching heaps. (C) 2016 Elsevier B.V. All rights reserved.</p

Comparison on the leaching kinetics of chalcocite and pyrite with or without bacteria

The acid leaching, ferric leaching, and bioleaching of chalcocite and pyrite minerals were conducted in two sets of 3L stirred reactors The dissolution rates of copper and iron were correlated with leaching conditions In the acid leaching process, the dissolution rate of chalcocite was around 40wt % while that of pyrite was less than 4% In the ferric leaching process with high ferric concentration, only 10 wt % of iron in pyrite was leached out at the same retention time though the copper recovery over 60 wt % in chalcocite For the bioleaching process the chalcocite leaching rate was highly increased, nearly 90 wt % of copper was leached out, and the iron dissolution of pyrite exceeded 70 wt % For the two minerals the bioleaching shows the highest leaching rate compared with the acid leaching or ferric leaching In uncontrolled bioleaching process pyrite could be dissolved effectively The experimental data were fitted to the shrinking core and particle model The results show that in all the leaching tests, the chalcocite leaching was mainly controlled by diffusion, while for the pyrite leaching chemical reaction is the main rate-determining ste

Investigation on the correlation between ferrous ion and the floatability of pyrite with different oxidation degrees

This work aims to establish the quantitative relationship between the surface oxidation state of pyrite and flotation performance. In this paper, an efficient method was proposed to prepare pyrite with different oxidation degrees. Flotation tests show that the floatability of pyrite decreased with prolonging the oxidation time. TofSIMS results reveal that the main component on the oxidized pyrite surface is Fe hydroxides or oxides. XPS analysis confirms that Fe(OH)2 and FeOOH are the main formula of Fe species, and the ratio of Fe2+/Total Fe agrees well with the floatability of pyrite with different oxidation degrees, which can be taken as an index to develop the flotation performance of pyrite. DFT simulation calculation further demonstrates the reliability of Fe (OH)2 as the active site. This study provides essential surface chemistry evidence for correlating the surface species with the floatability of pyrite with different oxidation states through quantitative analysis of various intermediate products

sulfidemineraldissolutionmicrobescommunitystructureandfunctioninindustrialbioleachingheaps

Heap bioleaching is one of the most clean and economical processes for recovery of low-grade and complex ores, because the sulfide minerals are natural habitats for acidophiles capable of iron-and sulfur-oxidation. The most exciting advances in heap bioleaching are occurring in the field of microbiology, especially with the development of advanced molecular biology approaches. These chemolithotrophic microorganisms living in the acid mine environment fix N2 and CO2 and obtain energy for growth from soluble ferrous iron and reduced inorganic sulfur compounds during oxidation of sulfide minerals. The ferric iron as oxidant and sulfuric acid are a result of microbial activity and provide favorable conditions for the dissolution of sulfide minerals. Various microbial consortia were applied successfully in commercial bioleaching heaps around the world, and microbial community and activity were adapted related to the local climatic conditions, ore characteristics and engineering configuration. This review focuses on diversity of bioleaching microbes, their role in heap bioleaching processes, their community structure and function in industrial heaps and the relation to the ore characteristics and the engineering configuration, to give implications for optimizing leaching efficiency of heap bioleaching