Next Article in Journal
Mineral Chemistry of Low-Temperature Phyllosilicates in Early Paleozoic Metaclastic Rocks, Eastern Tauride Belt, Türkiye
Previous Article in Journal
Magnetotelluric Noise Attenuation Using a Deep Residual Shrinkage Network
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Minerals
Volume 12
Issue 9
10.3390/min12091087
minerals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Reuse of Acid Bioleachate in Bacterial Oxidation of a Refractory Gold Sulfide Concentrate

by
Sitraka Herizo Andrianandraina
1,
Houshang Darvishi-Alamdari
1 and
Jean-François Blais
2,*
1
Département Génie des Mines, Métallurgie et Matériaux, Université Laval, 1036, Avenue de la Médecine, Québec City, QC G1V 0A6, Canada
2
Centre Eau Terre Environnement, Institut National de la Recherche Scientifique, Québec City, QC G1K 9A9, Canada
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(9), 1087; https://doi.org/10.3390/min12091087
Submission received: 15 July 2022 / Revised: 22 August 2022 / Accepted: 24 August 2022 / Published: 28 August 2022
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
Browse Figures
Review Reports Versions Notes

Abstract

:
Bacterial pre-oxidation of refractory gold concentrates generates large volumes of leachate and requires a significant supply of nutrients to support bacterial growth. Therefore, bioleachate reuse reduces both water consumption and the nutrients required for the process. However, the efficiency of this method and its benefit need to be further explored. In the present study, two tests on the reuse of bioleachate in new cycles of bacterial oxidation were carried out to evaluate the efficiency and the benefit of bioleachate reuse. Our results showed that the reuse of bioleachates could reduce nitrogen and phosphorus requirements by 40% and 36%, respectively, after a 14-day biooxidation stage in a stirred tank bioreactor. We also showed that the reuse of bioleachate had a positive effect on the recovery of gold in a subsequent 48 h treatment by cyanidation. The gold recovery rate (initial concentration of 44 mg/kg) remained unchanged at 90% after the two bioleachate recirculation loops. The reuse of bioleachate also made it possible to increase the solubilization rates of other metals from the sulfide concentrate. Thus, the solubilization yields of copper (initial concentration of 3587 mg/kg) and zinc (initial concentration of 27,315 mg/kg) increased, respectively, from 14.8% and 40.2% to 37.5% and 99.6% after the two bioleachate recirculation loops.

1. Introduction

Bacterial oxidation is one method used to pre-treat refractory gold sulfide concentrates [1]. The acid bioleachate resulting from the bacterial oxidation generates liquid effluent, concentrated in metals, which must be treated before being discharged [2]. The reuse of these bioleachates, although still little practiced, could help reduce costs and make the bacterial oxidation process even more helpful.
Bioleachates comprise metals/metalloids, such as iron and arsenic, as well as sulfuric acid. Iron is present in the ferric state (Fe3+), as ferric sulfate (Fe2(SO4)3). Arsenic is present in the arsenate state (As5+), as arsenic acid (H3AsO4). One of the potential issues encountered with the reuse of bioleachate is the accumulation of some toxic oxidation products, such as heavy metals, in the reused bioleachate. Some of these metals can be highly toxic, and bacterial cells, responsible for the leaching activity, may lose their metabolic activity [3]. The accumulation of toxic oxidation products can progressively inhibit bacteria and is likely to lead to a decrease in the efficiency of mineral oxidation [4]. Tuovinen et al. [5] showed that Acidithiobacillus ferrooxidans is sensitive to zinc, copper, nickel, cobalt, manganese and aluminum ions at concentrations above 10 g/L. The inhibition effect of bacterial activity for tellurium, arsenic, silver and selenium anions may start at concentrations between 0.05 and 0.10 g/L [4].
During bacterial oxidation, nitrogen (N) and phosphorus (P) are the two main nutrients used by microorganisms and must be supplied to the pulp [6,7]. In addition to their consumption for the metabolic needs of bacterial cells, these nutrients can be lost through the formation of the secondary precipitations of ammoniojarosite during the pre-oxidation step [8,9]. These precipitates can also act as physical barriers, slowing down the diffusion of leaching agents to the surface of sulfide particles where the main bacterial activity takes place [10]. These secondary precipitation products can also significantly increase the amount of metallic sludge to be managed, thus increasing the cost associated with its dewatering and disposal [11,12,13].
To reuse bioleachate in bacterial oxidation cycles, some solubilized heavy metals must also be removed to keep the bacteria active. The presence of ferric iron in the bioleachate can form a secondary precipitation, such as jarosite, which inhibits the bacterial oxidation of sulfide. The removal of heavy metals is normally performed by precipitation [14]. The molar ratio of iron and arsenic, as well as base metals, such as zinc, copper and cadmium in the bioleachate, determine the stability of the iron hydroxide precipitate [15]. For example, the higher the iron/arsenic ratio, the more stable the precipitate.
Bioleachate can be treated by precipitating metals as insoluble hydroxides using precipitating agents such as sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), magnesium hydroxide (Mg(OH)2) or alkali metal sulfides. The most used precipitating agents containing sulfur are CaS, Na2S [16,17], hydrosulfide of sodium (NaHS) and sodium thiosulfate (Na2S2O3) [17,18,19]. However, the precipitation of heavy metals using sulfur-containing agents poses an environmental hazard because of the risk of the emission of toxic hydrogen sulfide [18]. Using NaOH, although it is more expensive than hydrated lime (Ca(OH)2), to treat bioleachate has some advantages [20]. Bioleachates treated with NaOH are easier to dehydrate compared to bioleachates treated with Ca(OH)2, which also results in secondary precipitation products, such as gypsum and jarosite [8,9,10]. The formation of these two secondary products can negatively affect the process cost, including costly dewatering and sludge disposal steps [11,12,13].
In this study, bioleachates from the bacterial oxidation of a refractory gold sulfide concentrate are treated by removing ferric iron from the solution using sodium hydroxide (NaOH) as the precipitating agent and then reused twice in new cycles of bacterial oxidation. The effectiveness of this reuse of bioleachates is verified by evaluating the quantity of metals dissolved in the two reused bioleachates and in the yield of dissolution of the gold.

2. Materials and Methods

2.1. Preparation and Characterization of Refractory Gold Sulfide Concentrate

A sample of a refractory gold sulfide concentrate was obtained from a flotation operation, using potassium amyl xanthate (KAX) (40 mg/L) as a collector and methylisobu-tilcarbinol (MIBC) (2 mg/L) as a foaming agent. The pH was adjusted to 5.5 by adding NaOH or H2SO4 [21]. The concentrate comprised polymetallic sulfides. X-ray diffraction (XRD) was used to identify the main mineral phases present in the sample. The chemical characterization of the sample was carried out by ICP-AES. Elemental composition of gold sulfide concentrate is shown in Table 1. The particle size used in all bacterial oxidation tests was D80 at 12 µm.

2.2. Bacterial Pre-Oxidation

The bacterial pre-oxidation process was the same as that described to treat refractory gold by Andrianandraina et al. [21]. Briefly, a 5% inoculum of a mixed population of Acidithiobacillus ferrooxidans (ATCC19859) and Acidithiobacillus thiooxidans (ATCC19377) was used as the bacteria source. To maintain these microorganisms in an active state, 4.31 g/L (NH4)2SO4 and 0.71 g/L K2HPO4 were added as a source of nitrogen and phosphorus. The initial pH was adjusted to 1.7 by adding sulfuric acid. The temperature was maintained at 30 ± 2 °C using a water bath system. The pulp was agitated at 120 rpm using an axial propeller to ensure that all particles remained in suspension. An aeration rate of two volumes of air per one volume of liquid per minute (vvm) was used in the biooxidation experiments. The experiments were carried out in batches and in a small transparent acrylic bioreactor (10 cm in diameter, 20 cm in height) with a capacity of 1 L. The pulp density was set at 20%.

2.3. Reuse of Bioleachates

The main steps in the reuse of bioleachate for bacterial oxidation are summarized in Figure 1. The first step (Biooxidation 1) comprised producing an initial bioleachate (Bioleachate 1) from a bacterial oxidation test. The solid part (Concentrate 1) was then separated from the liquid by filtration and kept for the cyanidation step. Bioleachate 1 was treated at pH = 4.0 using sodium hydroxide (15 g/L) to precipitate the iron in the solution, i.e., Bioleachate treatment 1. The resulting liquid was used in the subsequent step (Biooxidation 2) to pre-oxidize the gold sulfide concentrate. After this bacterial oxidation, the solid fraction (Concentrate 2) was separated from the liquid fraction (Bioleachate 2). The solid residue was kept for the cyanidation test and the aqueous phase again retreated with NaOH (15 g/L) to precipitate the iron. The operation was repeated for the second reuse of the bioleachate, i.e., Biooxidation 3, which resulted in the production of Bioleachate 3 and Concentrate 3. The cyanidation treatment made it possible to see the impact of the reuse of the treated bioleachate on bacterial oxidation performance and gold dissolution. Of the three bioleachates, 10 mL of each was taken for chemical analysis. The reuse of bioleachate saves the reagents used in the biooxidation of sulfides. To maintain the growth of microorganisms, it is sufficient to add only a few essential reagents, such as ammonium (NH4+), as a source of nitrogen, and phosphate (PO43−), as a source of phosphorus.

2.4. Iron Precipitation

The presence of iron in the bioleachate at acidic pH (pH = 1.6) can form different precipitates, such as natrojarosite and ammoniojarosite. To minimize the formation of these different precipitates, iron should be precipitated before the reuse of bioleachate. To determine the optimum pH value for iron precipitation, eight precipitation tests were performed using 50 mL of Bioleachate 1 in 125 mL Erlenmeyer flasks with different pH values of 3.2, 3.4, 3.6 and 4.0. Sodium hydroxide (10–15 g NaOH/L) was used as a precipitating agent. The amount of NaOH necessary to precipitate the iron was calculated using the precipitation reaction between the sodium hydroxide solution and the Fe3+ ion Equation (1).
6 NaOH + Fe2(SO4)3 → 2 Fe(OH)3 + 3 Na2SO4
To complete the precipitation reaction and avoid the overconsumption of hydroxyl ion (OH−) by the sulfuric acid, NaOH was diluted with distilled water and then poured drop wise into an ampoule to settle during the precipitation reaction. After precipitation, the solutions were vacuum filtered using a Whatman G6 fiberglass membrane (porosity: 1–3 µm). The solid fraction was dried in an oven and weighed. The liquid fraction was acidified with 5% HNO3 for its conservation until the analysis of the dissolved chemical elements by ICP-AES. Equation (2) was used to calculate iron removal efficiency in biological leachate.
Iron removal efficiency (%) = 100 × ([Fe]initial − [Fe]final)/[Fe]initial
where the [Fe]initial and [Fe]final are the initial and final concentrations of iron in the bioleachate.
Bioleachate 1 was treated for iron removal by using NaOH as the precipitating agent. Figure 2 shows the evolution of the iron concentration in Bioleachate 1 as a function of the increase in pH because of the addition of a NaOH solution. The iron removal efficiencies at different pH values of 3.2, 3.4, 3.6 and 4.0 were 94.7 ± 0.7%, 98.1 ± 0.2%, 99.2 ± 0.2% and 99.9 ± 0.1%, respectively. The pH value of 4.0 was chosen as the best condition for iron removal, which resulted in an iron concentration of only 2.2 mg/L in the treated solution. The selection of pH = 4 is consistent with the work of Halder et al. [22] who used Ca(OH)2 to precipitate iron. Santaolalla et al. [17] also showed that ferric iron precipitates efficiently at pH = 4.
Bioleachate 1 was therefore treated for iron removal at pH = 4. The first treatment, i.e., Bioleachate treatment 1, was carried out using 1 L of bioleachate, where a concentration of 2.23 mg/L of iron was measured in the solution (Table 2). A precipitate sample with a dry mass of 3.76 g was also obtained per liter of bioleachate. The result obtained in this work agrees with those published by Choo et al. [23]. The ratio of the weight of the precipitate to the added sodium hydroxide was 0.3. This ratio is proportional to 1 mole of NaOH, which is equal to three times the number of moles of iron, since ferric iron is the main ionic form of the iron present in the bioleachate. A Fe3+ ion reacts with three OH− ions to form an iron precipitate as ferric hydroxide (Fe(OH)3).
The second treatment, i.e., Bioleachate treatment 2, was performed using 1 L of Bioleachate 2. The amount of NaOH used to precipitate iron and the pH value used were the same as in the first treatment test (Table 2). The sludge generated contained 6.37 g of precipitate per litter of bioleachate. The iron concentration remaining in Bioleachate 2 after the second precipitation test was 59.3 mg/L, which represents 98.2% iron removal. The weight ratio of the precipitate to sodium hydroxide added was 0.5. The amount of iron precipitated by the Bioleachate 2 treatment was almost twice the amount of iron precipitated during the first treatment. This difference is explained by the different concentrations of iron in Bioleachate 1 and Bioleachate 2, which were, respectively, 1477 mg/L and 3349 mg/L.

2.5. Batch Cyanidation

After the bacterial oxidation, the solid fraction was separated from the liquid fraction. The solid residue obtained was aerated for 1 h while maintaining a concentration of 8 mg/L of dissolved oxygen, then cyanidated at 20 °C. A sodium cyanide concentration of 706 mg/L was introduced to obtain a cyanide concentration of 500 mg/L CN−. A pulp density of 10% solids was used for the cyanidation tests. This cyanidation work is more detailed in the work carried out on the treatment of refractory gold by Andrianandraina et al. [21].

2.6. Sample Analysis

The pH, temperature and oxidation reduction potential (ORP) were measured simultaneously using a Fisher Scientific XL 60D Accumet Excel. ORP measurements were performed by using Ag/AgCl reference electrode with an electrode potential of 199 mV vs. standard hydrogen electrode. The dissolved oxygen concentration was determined using a Hach HQ40d portable counter. To determine the metal content of the sulfide concentrate, a total digestion in hydrofluoric acid (HF) was first required. Analyses of the main metals constituting the solid concentrates were carried out using XRD and ICP-AES (Andrianandraina et al., 2021) [21]. A PANalytical-Aeris CuKα diffractometer was used for the analysis. Identification and semi-quantitative determination of the different crystalline phases were achieved by comparing the XRD diffractograms. The diffractogram peaks were interpreted using HighScore Plus software, and the major and minor phases of the sample were semi-quantified [24]. Semi-quantification of the identified species was performed using the Rietveld method [25]. The chemical characterization of the liquid samples was performed using ICP-AES (Vista-AX CCO, Palo Alto, CA, USA). NH4-N and PO4-P were measured using a Lachat Flow Injection Analyzer (model 8000 Series, Zellweger Analytics) (NH4-N: QuikChem® Method 10-107-06-2-B; PO4-P: QuikChem® Method 10-115-01-1-B). Analysis of dissolved gold during cyanidation was performed by the MP-AES microwave plasma atomic emission spectrometry technique (Agilent, model 4100+).

3. Results and Discussion

3.1. Initial Composition of the Gold Sulfide Concentrate

The initial composition of the refractory gold sulfide concentrate is shown in Table 1. The concentrate contains high levels of iron (11.3%), lead (7.83%), barium (7.75%) and zinc (2.73%). Chromium, nickel and copper are also found with respective concentrations of 1.34%, 0.73% and 0.36%. Precious metal contents are obviously high, with the initial contents of 44 mg/kg and 18.9 mg/kg for gold and silver, respectively.
XRD analyses revealed the major presence of silica (SiO2), pyrite (FeS2), galena (PbS), chalcopyrite (CuFeS2), sphalerite (ZnS) and barite (BaSO4).

3.2. Bioleachate 1

The concentrations of dissolved elements present in Bioleachate 1 are presented in Table 2. The results show very high concentrations of sulfur (4277 mg/L), iron (1477 mg/L) and zinc (1097 mg/L). The high sulfur concentration is explained by the generation of sulfuric acid (H2SO4) by microorganisms as a by-product of bacterial oxidation of sulfides. The formation of sulfuric acid decreases the pH of the stock solution from 1.7 to pH = 1.6 (Table 2). This result is consistent with those reported by Leng et al. [26] on the bacterial pre-oxidation of a gold sulfide concentrate.
The high ORP value of 530 mV (Table 2) shows that the iron in the solution is mainly ferric ion, following the oxidation of the ferrous ion by Acidithiobacillus ferrooxidans [27]. The high concentration of zinc in the solution is explained by the biooxidation of sphalerite (ZnS), a sulfide that is easily oxidized by microorganisms [28].

3.3. Metals’ Solubilization

During the first bacterial pre-oxidation test, the solubilization percentages of iron (Fe), sulfur (S) and zinc (Zn) were, respectively, 21.9%, 38.0% and 40.2%. The solubilization of these three elements was calculated in relation to the concentration of the elements in the concentrate, i.e., the ratio between the mass of dissolved elements in the bioleachate and the mass of elements in the concentrate multiplied by 100. These solubilizations increased in Bioleachate 2 with the respective values of 29.8%, 64.3% and 94.6% (Figure 3 and Figure 4). These solubilization yields increased further in Bioleachate 3 with the respective values of 36.4%, 89.1% and 99.6%. The increase in the activity of microorganisms producing sulfuric acid during the reuse of Bioleachate 1 and Bioleachate 2 caused these increases. The addition of 5% bacterial inoculation at each reuse may increase the quantity of microorganisms present in the bioleachate, which could explain the increase in bacterial activity. In addition, the microorganisms initially present in the bioleachate are already well acclimated to the sulfides, yielding the decrease in the latency time of the microorganisms. As shown in Table 2, a decrease in the pH value (pH = 1.6) in Bioleachate 2 and Bioleachate 3 was also noticed compared to Bioleachate 1 (pH = 1.7). After treatment with NaOH, the bioleachate had a pH = 4 and then adjusted to pH = 1.7 before starting the reuse. After 14 days of bacterial oxidation, the pH of the bioleachate decreased to pH = 1.5.
Figure 4 compares the dissolution progress of Fe and S of the refractory gold sulfide concentrate over 14 days for the three successive bacterial pre-oxidation tests. The iron concentration of Bioleachate 1 increased steadily over 14 days to reach a final concentration of 1477 mg/L. The iron concentration in Bioleachate 2 seemed to be stabilized after 4 days, while that of Bioleachate 3 reached a plateau after 8 days. It is interesting to note that the final concentration of iron in bioleachates increased with their reuse, i.e., 1477 mg/L for Bioleachate 1 compared to 3926 mg/L for Bioleachate 3. The addition of an extra 5% of bacterial inoculation in the bioleachate could explain this increase. It should also be emphasized that the subsequent bioleachates were treated to remove iron, and this is the reason the initial concentration of all bioleachates started at almost zero up to a final value of 3926 mg/L.
Similarly, an appreciable increase in the final concentration of soluble sulfur was noted during these tests, i.e., from 4277 mg/L for Bioleachate 1 compared to 12,645 mg/L for Bioleachate 3. Figure 4 shows that the increase in the solubilization of iron and sulfur in the solution was notable after only 4 days of reaction. Thus, the reuse of bioleachate seemed to accumulate many sulfates. Other precipitates associated with the iron precipitates could reduce the accumulation of sulfur during the iron precipitation.
The increase in zinc solubilization could also be of electrochemical origin, i.e., by the galvanic interaction between pyrite and sphalerite particles [29]. Pyrite, less soluble than sphalerite, acts as a redox catalyst (i.e., an electron acceptor) by providing an additional surface for electronic transfer to ferric ions and establishes a galvanic coupling with sphalerite (the electron donor) to speed up its dissolution [30,31]. Indeed, the solubilization of Zn depends on the amount of Fe3+ ions in the bioleachate because it is the Fe3+ ion that attacks zinc. In Bioleachate 2 and Bioleachate 3, the concentration of dissolved iron was higher than in Bioleachate 1. This may show that the reuse of bioleachate could improve the solubilization of other metals as well.
The solubilization of chromium (Cr), nickel (Ni) and lead (Pb) was low and did not exceed 5% during the three successive bacterial pre-oxidation tests (Figure 3). Cr and Ni were probably associated with the silicate matrix, which was less attacked by the sulfuric acid produced by the bacteria. Regarding Pb, even if it is found mainly associated with galena (PbS), lead sulfate is poorly soluble, which makes it unfavorable to be dissolved by microbial leaching [2].
With copper (Cu), its solubilization was low (14.8%) in Bioleachate 1; then, it increased (24.9% and 37.5%) in the two bioleachates from the two reuse tests (Figure 3). The attack of Fe3+ ions, as a strong oxidizing agent generated by the bacterial oxidation of sulfides, can explain the increase in the solubilization of copper in the reused bioleachates [32].
Since the ferric iron precipitation at pH = 4.0 was selective, there were still some amounts of dissolved heavy metals left in the bioleachate. Repeated reuse of bioleachate builds up concentrations of dissolved metals in solution. In this study, the concentrations of metals, such as Al, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in the bioleachate were analyzed by ICP-AES. The results are shown in Table 2. The highest concentrations of metals were found in Fe and Zn, whose quantity increased with the number of bioleachate reuse. For bioleachate 1, bioleachate 2 and bioleachate 3, the concentrations of Fe and Zn were 1477 mg/L; 3349 mg/L; 3926 mg/L and 1097 mg/L; 3107 mg/L; 3861 mg/L, respectively. Excessive accumulation of these metals in bioleachate may limit the activities of microorganisms to dissolve metals. These dissolved metals, such as Zn, Pb, Ni, Mn, Cu, Cr, Co, Al and Ag, can become toxic to microorganisms if their concentration in the solution is high [5]. The results presented in Table 2 show, however, that the increase in dissolved metal concentrations was moderate and did not significantly affect the growth of microorganisms, given the very good sulfide oxidation activity noted during the second bioleachate reuse test. Zinc is a non-ferrous metal with the highest increase in concentration with a value of 3.86 g/L at the end of the second bioleachate reuse test. It would even be interesting to assess the economic profit in recovering this metal after a certain number of bioleachate reuse cycles. Solvent extraction techniques, combined with electrodeposition, would be potentially interesting to concentrate and purify this metal [33,34].
The high amounts of iron and sulfur in reused bioleachate resulted in a more rapid destruction of the sulfide matrix and exposure of the gold encapsulated in it [35]. Since the reuse of bioleach increases the amount of dissolved metals during the sulfide pre-treatment, it can also decrease the residence time of the pulp in the bacterial oxidation tanks and significantly reduce the operating and capital cost of equipment prior to cyanidation. In addition, the reuse of bioleachate is beneficial for the maintenance of bacterial activity during bacterial oxidation because of the strong sorption of certain toxic elements for microorganisms, such as arsenic, in the iron oxyhydroxide residue [35]. Indeed, the reuse of bioleachate in a bacterial oxidation cycle could decrease the adaptation time of the microorganisms with the sulfide concentrate before multiplying in the reactor.

3.4. Nutrients Availability

Table 3 shows the associated benefits of saving reagents (K, Mg, Ca) when reusing bioleachate. Reuse allows the addition of only a few essential reagents to maintain the growth of microorganisms. The two essential reactive components envisaged to be added to bioleachate for all reuses are ammonium (NH4+), as a source of nitrogen, and phosphate (PO43−), as a source of phosphorus, to ensure the optimal growth of microorganisms [36]. The decrease in the ammonium and phosphate concentrations during biooxidation treatment can be explained by the formation of jarosite precipitate XFe3(SO4)2(OH)6 where X is a variable and can comprise Na+ (Natrojarosite), K+ (Potasium jarosite), NH4+ (Ammoniojarosite). Phosphate can also be lowered by the precipitation of ferric phosphate.
The treated bioleachates initially contained most of the nutritional elements necessary to maintain the survival of the microorganisms. Only the addition of nitrogen and phosphorus to the bioleachate is necessary before its reuse. The obtained results presented in Table 3 show that the NH4-N value in untreated bioleachates 1, 2 and 3 was increased. This increase could be explained by the addition of 5% bacterial inoculum during the reuse of each of these bioleachates. However, after treatment of the bioleachates, a significant decrease in NH4-N of bioleachates 1 and 2 was observed. This decrease could be explained by the formation of ammoniojarosite. For the PO4-P value in bioleachate 1, there was a noticeable decrease in its value from 126 to 42.6 mg/L. This decrease could be explained by the precipitation of ferric phosphate in the biooxidation 1 test. The addition of nitrogen and phosphorus and the 5% bacterial inoculation at each bioleachate reuse test could, however, explain the increase in PO4-P in the second and third biooxidation tests. In addition, the sulfide concentrate used initially contained 96 mg/kg phosphate.
Regarding potassium (K), this comes both from the ore and from the supply of KH2PO4, used as a source of phosphate. The concentration of this element in the solution increased during the three bacterial oxidation tests. This can be explained by a high content of K in the concentrate, which can be solubilized under acidic conditions. However, a decrease in K during the treatment of the bioleachates was observed, which could be caused by the formation of the potassium jarosite. The concentration of magnesium (Mg) in the three bioleachates was relatively unaffected by the reuse process. This element is solubilized from the carbonate magnesium minerals present in the processed ore [21]. As for calcium (Ca), there was a progressive increase in the bioleachates, which could be explained by a high concentration of Ca in the concentrate.

3.5. Cyanidation Test

Figure 5 illustrates the kinetics of gold solubilization during the cyanidation tests of the three concentrates, having undergone the bacterial pre-oxidation step. The solubilization curves are practically similar, and the final yields after 48 h of cyanidation are very similar, i.e., 90.5%, 90.2% and 89.8% for Concentrate 1, Concentrate 2 and Concentrate 3, respectively.
Some ions, such as iron, copper, cobalt, nickel, zinc, can consume cyanide during gold cyanidation. Mubarok et al. [37] reported that the high consumption of sodium cyanide (NaCN) during cyanidation of bioleached residue is due to the redissolution of sulfur and iron that are precipitated during bacterial oxidation and reacted with the cyanide ion to form thiocyanate and ferrocyanide complexes. If these heavy metals can be minimized before cyanidation, the cyanide consumption can be reduced. In this study, the result of reuse of bioleachates in new cycles of bacterial oxidation of a refractory gold sulfide concentrate showed a significant increase in some dissolved heavy metals from the sulfide concentrate. Indeed, the high amounts of certain dissolved heavy metals in the bioleachates means that the concentration of heavy metals in the bioleachate residue (solid fraction intended for cyanidation) also decreases. This could explain the decrease in cyanide consumption during bioleachate reuse.
The works of Ciftci and Akcil [38] on the bacterial oxidation of refractory gold with the extreme thermophilic bacterium produced similar results, and they obtained 92% of the dissolved gold after cyanidation with a consumption of 17.5 kg per ton of sodium cyanide. However, the cost associated with the optimal growth temperature of this bacteria may decrease the efficiency of its use in a refractory gold bacterial oxidation process. Pulp density may also limit the use of this extreme thermophilic bacterium because its oxidation reaction is exothermic. Since the dissolution of refractory gold sulfide is a slow process, it is therefore necessary to find a technique to speed up it. The contribution of Ahna et al. [39] to the improvement of bacterial oxidation using the sand farming process has yielded significant results, with 96% of refractory gold recovery. This reduces the costs associated with grinding and reagents. However, the pre-oxidation time before cyanidation is long, including 83 days in a batch reactor. The works of Carvalho et al. [1] on pretreatment of refractory gold by bacterial oxidation also showed a long pre-oxidation time of 40 days, with 85% gold recovery after cyanidation with a D100 particle size of 37 μm. Our results show bioleachate reuse may contribute to improving the recovery of refractory gold. After 14 days of bacterial pre-oxidation in a batch reactor, about 90% of the gold was dissolved after 48 h of cyanidation, while the direct cyanidation was only 68% [21]. This result could be further improved by extending the bacterial pre-oxidation time from 16 to 20 days.

4. Conclusions

The reuse of bioleachates during the bacterial oxidation of refractory gold sulfide concentrate was evaluated in this study. The results revealed that the reuse of bioleachates accumulates the quantities of dissolved elements despite the application of a ferric iron precipitation treatment at pH = 4.0. The microorganisms responsible for dissolving metal sulfides are more active when reusing bioleachates than when using a new culture medium. The presence of certain dissolved metals in the reused bioleachate exerts a positive influence on the dissolution of other metals. Nitrogen and phosphorus are the only two nutrients to be added to bioleachate when it is reused. In addition, we showed that the gold dissolution yield by cyanidation of microbially treated sulfide is 90%, with or without the reuse of bioleachates. Through this study, we showed that the reuse of bioleachate has positive impacts on the overall performance of bacterial oxidation, representing a great potential to save water and chemical reagents.

Author Contributions

Conceptualization, Methodology, Investigation, Formal Analysis, Writing—original draft: S.H.A.; Funding acquisition, Project administration: H.D.-A.; Supervision, Writing—review and editing: H.D.-A. and J.-F.B. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to thank the CFSP-CBIE for supporting the first author with a scholarship.

Data Availability Statement

The relevant datasets analyzed in this study are all presented in the manuscript.

Acknowledgments

We thank Vicky Dodier for technical support during the sample preparation and gold assaying at the University of Laval laboratory, and Geneviève Rioux for technical support during the biooxidation process at the INRS laboratory, and Lan Huong Tran for chemical analysis.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Carvalho, L.C.D.; Silva, S.R.D.; Marra, R.; Giardini, N.; Souza, L.F.C.D.; Leão, V.A. Bio-oxidation of refractory gold ores containing stibnite and gudmundite. Environ. Technol. Innov. 2019, 15, 11. [Google Scholar] [CrossRef]
  2. Couillard, D.; Mercier, G. Précipitations sélectives des métaux solubilisés biologiquement de boues aérobies d’épuration. Can. J. Chem. Eng. 1992, 70, 1021–1029. [Google Scholar] [CrossRef]
  3. Roy, J.J.; Srinivasan, M.; Cao, B. Biooxidation as an eco-friendly approach for metal recovery from spent NMC-based lithium-ion batteries at a high pulp density. ACS Sustain. Chem. Eng. 2021, 9, 3060–3069. [Google Scholar]
  4. Bailey, A.D.; Hansford, G.S. Factors affecting bio-oxidation of sulfide minerals at high concentrations of solids: A review. Biotechnol. Bioeng. 1993, 42, 1164–1174. [Google Scholar] [CrossRef] [PubMed]
  5. Tuovinen, O.H.; Niemela, S.I.; Gyllenberg, H.G. Tolerance of Thiobacillus ferrooxidans to some metals. Antonie Van Leeuwenhoek 1971, 37, 489–496. [Google Scholar] [CrossRef]
  6. Blais, J.F.; Meunier, N.; Mercier, G.; Drogui, P.; Tyagi, R.D. Pilot plant study of simultaneous sewage sludge digestion and metal leaching. J. Environ. Eng. 2004, 130, 516–525. [Google Scholar] [CrossRef]
  7. Pathak, A.; Dastidar, M.G.; Sreekrishnan, T.R. Biooxidation of heavy metals from sewage sludge: A review. J. Environ. Manag. 2009, 90, 2343–2353. [Google Scholar] [CrossRef]
  8. Kaksonena, A.H.; Morrisa, C.; Lib, J.; Wyliea, J.; Ushera, K.; Hilarioc, F.; Plessisd, C. The fate and impact of contaminants in a biological iron oxidation and jarosite precipitation process. Miner. Eng. 2019, 132, 258–267. [Google Scholar] [CrossRef]
  9. Nurmi, P.; Özkaya, B.; Sasaki, K.; Kaksonen, A.H.; Riekkola-Vanhanen, M.; Tuovinen, O.H.; Puhakka, J.A. Biooxidation and precipitation for iron and sulfate removal from heap biooxidation effluent streams. Hydrometallurgy 2010, 101, 7–14. [Google Scholar] [CrossRef]
  10. Rabbani, M.; Ahmadi, A. Simultaneous removal of iron and sulfate from biodesulfurization solutions of a coking coal by jarosite precipitation. J. Water Process Eng. 2020, 38, 101678. [Google Scholar] [CrossRef]
  11. Alves, L.D.C.; Cammarota, M.C.; França, F.P.D. Reduction on the anaerobic biological activity inhibition caused by heavy metals and sulphates in effluents through chemical precipitation with soda and lime. Environ. Technol. 2006, 27, 1391–1400. [Google Scholar] [CrossRef] [PubMed]
  12. Blais, J.F.; Dufresne, S.; Mercier, G. État du développement technologique en matière d’enlèvement des métaux des effluents industriels. J. Water Sci. 1999, 12, 687–711. [Google Scholar] [CrossRef]
  13. Tatangelo, A. Optimisation de la précipitation des métaux lourds en mélange et valorisation des boues d’hydroxydes: Application aux effluents de traitement de surfaces. Ph.D. Thesis, École Nationale Supérieure des Mines de Saint-Etienne, Saint-Étienne, France, 2013; p. 293. [Google Scholar]
  14. Therdkiattikul, S. Treatment Methods, Safe Contaminants Precipitate Disposal and Water Reclamation, and Recycling of Effluents from Bacterial Leaching of Precious Metals Refractory Ores. Ph.D. Thesis, The University of Utah, Salt Lake City, UT, USA, 1996. [Google Scholar]
  15. Nyombolo, B.M.; Neale, J.W.; Staden, P.J. Neutralization of bioleach liquors. J. S. Afr. Inst. Min. Metall. 2000, 100, 403–408. [Google Scholar]
  16. Blais, J.F.; Djedidi, Z.; Cheikh, R.B.; Tyagi, R.D.; Mercier, G. Metals precipitation from effluents: Review. Pract. Period. Hazard. Toxic Radioact. Waste Manag. 2008, 12, 135–149. [Google Scholar] [CrossRef]
  17. Santaolalla, A.; Lens, P.N.L.; Barona, A.; Rojo, N.; Ocio, A.; Gallastegui, G. Metal extraction and recovery from mobile phone PCBs by a combination of biooxidation and precipitation processes. Minerals 2021, 11, 1004. [Google Scholar] [CrossRef]
  18. Pohl, A. Removal of heavy metal ions from water and wastewaters by sulfur-containing precipitation agents. Water Air Soil Pollut. 2020, 231, 503. [Google Scholar] [CrossRef]
  19. Thomas, M.; Kozik, V.; Bak, A.; Barbusinski, K.; Jazowiecka-Rakus, J.; Jampilek, J. Removal of heavy metal ions from wastewaters: An application of sodium trithiocarbonate and wastewater toxicity assessment. Materials 2021, 14, 655. [Google Scholar] [CrossRef]
  20. Kennedy, A.M.; Arias-Pai´c, M. Application of powdered steel slag for more sustainable removal of metals from impaired waters. J. Water Process Eng. 2020, 38, 101599. [Google Scholar] [CrossRef]
  21. Andrianandraina, S.H.; Dionne, J.; Darvishi-Alamdari, H.; Blais, J.F. Effect of grain size on the bacterial oxidation of a refractory gold sulfide concentrate and its dissolution by cyanidation. Miner. Eng. 2022, 176, 107360. [Google Scholar] [CrossRef]
  22. Halder, D.; Lin, J.; Essilfie-Dughan, J.; Das, S.; Robertson, J.; Hendry, M.J. Implications of the iron(II/III)-arsenic ratio on the precipitation of ironarsenic minerals from pH 2.5 to 10.5. Appl. Geochem. 2018, 98, 367–376. [Google Scholar] [CrossRef]
  23. Choo, T.K.; Etschmann, B.; Selomulya, C.; Zhang, L. Behavior of Fe2+/3+ cation and its interference with the precipitationof Mg2+ cation upon mineral carbonation of Yallourn fly ash leachate under ambient conditions. Energy Fuels 2016, 30, 3269–3280. [Google Scholar] [CrossRef]
  24. Degen, T.; Sadki, M.; Bron, E.; König, U.; Nénert, G. The HighScore suite. Powder Diffr. 2014, 29, S13–S18. [Google Scholar] [CrossRef] [Green Version]
  25. Rietveld, H.M. A profile refinement method for nuclear and magnetic structures. J. Appl. Crystallogr. 1969, 2, 65–71. [Google Scholar] [CrossRef]
  26. Leng, F.; Li, K.; Zhang, X.; Li, Y.; Zhu, Y.; Lu, J.; Li, H. Comparative study of inorganic arsenic resistance of several strains of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. Hydrometallurgy 2009, 98, 235–240. [Google Scholar] [CrossRef]
  27. Bevilaqua, D.; Lahti-Tommila, H.O.G.; Puhakka, J.A.; Tuovinen, O.H. Bacterial and chemical leaching of chalcopyrite concentrates as affected by the redox potential and ferric/ferrous iron ratio at 22 °C. Int. J. Miner. Processing 2014, 132, 1–7. [Google Scholar] [CrossRef]
  28. Balci, N.C. Effect of bacterial activity on trace metals release from oxidation of sphalerite at low pH (<3) and implications for AMD environment. Environ. Earth Sci. 2010, 60, 485–493. [Google Scholar] [CrossRef]
  29. Muravyov, M. Bioprocessing of mine waste: Effects of process conditions. Chem. Pap. 2019, 73, 3075–3083. [Google Scholar] [CrossRef]
  30. Estrada-de los Santos, F.; Rivera-Santillán, R.E.; Talavera-Ortega, M.; Bautista, F. Catalytic and galvanic effects of pyrite on ferric leaching of sphalerite. Hydrometallurgy 2016, 163, 167–175. [Google Scholar] [CrossRef]
  31. Marchevsky, N.; Urbieta, M.S.; Bernardelli, C.; Mas, M.; Donati, E.R. Zinc recovery during refractory ore biooxidation by an indigenous consortium. Int. J. Miner. Processing 2015, 138, 30–37. [Google Scholar] [CrossRef]
  32. Chen, W.; Yin, S.; Zhou, G.; Li, Z.; Song, Q. Copper recovery from tailings through biooxidation and further application of bioleached tailings residue: Comprehensive utilization of tailings. J. Clean. Prod. 2022, 332, 130129. [Google Scholar] [CrossRef]
  33. Tanong, K.; Tran, L.H.; Coudert, L.; Mercier, G.; Blais, J.F. Recovery of Zn from unsorted spent batteries using solvent extraction and electrowinning. J. Environ. Eng. Div. ASCE 2018, 144, 04018033. [Google Scholar] [CrossRef]
  34. Tanong, K.; Tran, L.H.; Mercier, G.; Blais, J.F. Recovery of Zn (II), Mn (II), Cd (II) and Ni (II) from the unsorted spent batteries using solvent extraction, electrodeposition and precipitation methods. J. Clean. Prod. 2017, 148, 233–244. [Google Scholar] [CrossRef] [Green Version]
  35. Hua, J.; Huang, H.; Xie, H.; Gand, L.; Liud, J.; Long, M. A scaled-up continuous process for biooxidation as pre-treatment of refractory pyrite-arsenopyrite gold-bearing concentrates. Biochem. Eng. J. 2017, 128, 228–234. [Google Scholar] [CrossRef]
  36. Morin, D.H.R. Biooxidation of sulfide minerals in continuous stirred tanks. In Microbial Processing of Metal Sulfides; Donati, E.R., Sand, W., Eds.; Springer: Dordrecht, The Netherlands, 2007; pp. 133–150. [Google Scholar] [CrossRef]
  37. Mubarok, M.Z.; Winarko, R.; Chaerun, S.K.; Rizki, I.N.; Ichlas, Z.T. Improving gold recovery from refractory gold ores through biooxidation using iron-sulfur-oxidizing/sulfur-oxidizing mixotrophic bacteria. Hydrometallurgy 2017, 168, 69–75. [Google Scholar] [CrossRef]
  38. Ciftci, H.; Akcil, A. Effect of biooxidation conditions on cyanide consumption and gold recovery from a refractory gold concentrate. Hydrometallurgy 2010, 104, 142–149. [Google Scholar] [CrossRef]
  39. Ahna, J.; Wua, J.; Ahnb, J.; Leea, J. Comparative investigations on sulfidic gold ore processing: A novel biooxidation process option. Miner. Eng. 2019, 140, 8. [Google Scholar] [CrossRef]
Minerals 12 01087 g001 550
Figure 1. Flowsheet of the reuse of bioleachate in the biooxidation process.
Figure 1. Flowsheet of the reuse of bioleachate in the biooxidation process.
Minerals 12 01087 g001
Minerals 12 01087 g002 550
Figure 2. Soluble iron concentration in Bioleachate 1 in function of the pH.
Figure 2. Soluble iron concentration in Bioleachate 1 in function of the pH.
Minerals 12 01087 g002
Minerals 12 01087 g003 550
Figure 3. Metals’ solubilization from the gold concentrate during the biooxidation process using new (Bioleachate 1) and reuse effluents (Bioleachate 2 and Bioleachate 3) as a culture medium.
Figure 3. Metals’ solubilization from the gold concentrate during the biooxidation process using new (Bioleachate 1) and reuse effluents (Bioleachate 2 and Bioleachate 3) as a culture medium.
Minerals 12 01087 g003
Minerals 12 01087 g004 550
Figure 4. Variation of iron (Fe) and sulfur (S) concentration in solution as a function of time during the bacterial oxidation process. (a): Iron; (b): Sulfur.
Figure 4. Variation of iron (Fe) and sulfur (S) concentration in solution as a function of time during the bacterial oxidation process. (a): Iron; (b): Sulfur.
Minerals 12 01087 g004
Minerals 12 01087 g005 550
Figure 5. Dissolution kinetic of gold by cyanidation of the concentrates treated by the bacterial oxidation process.
Figure 5. Dissolution kinetic of gold by cyanidation of the concentrates treated by the bacterial oxidation process.
Minerals 12 01087 g005
Table
Table 1. Elemental composition of gold sulfide concentrate.
Table 1. Elemental composition of gold sulfide concentrate.
ElementsContent
(mg/kg)		ElementsContent
(mg/kg)
Ag18.9Mn1165
Al8153Mo514
As75Na97
Au44Ni7338
Ba77,519P96
Bi<5Pb78,250
Ca1006S112,422
Cd306Sb30
Co29.1Sc0.7
Cr13,376Si201,138
Cu3587Sr1230
Fe112,517Ti358
K1553Th<0.5
Mg805V50
Zn27,315
Table
Table 2. Characteristics and chemical composition (mg/L) of the three bioleachates.
Table 2. Characteristics and chemical composition (mg/L) of the three bioleachates.
ParametersDLBioleachate 1Bioleachate 2Bioleachate 3
Non-TreatedTreatedNon-TreatedTreatedNon-Treated
pH 1.741.6741.6
ORP (mV) 538458520245570
Al0.0129.47.7147.410.243.4
Cr0.0236.50.550.6555.8
Cu0.0153.321.811171.5178
Fe0.0114772.23334959.33926
Mn0.0132.714.746.216.950.2
Na0.032693292363743835176
Ni0.0119.48.675329.453
Pb0.042.86113568135
S0.24277325410,489455112,645
Zn0.011097523310710463861
DL: Detection Limit.
Table
Table 3. Concentration (mg/L) of the soluble nutrients in the initial culture media and bioleachates.
Table 3. Concentration (mg/L) of the soluble nutrients in the initial culture media and bioleachates.
Medium Nutrients
NH4-NPO4-PKMgCa
Synthetic 9K media 91412614071010.0
Bioleachate 1Non-treated188242.6150123169
Treated4293.0 71.357.776.6
Bioleachate 2Non-treated1638284 398126188
Treated54314324847.744.8
Bioleachate 3Non-treated2004284 510114205
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Andrianandraina, S.H.; Darvishi-Alamdari, H.; Blais, J.-F. Reuse of Acid Bioleachate in Bacterial Oxidation of a Refractory Gold Sulfide Concentrate. Minerals 2022, 12, 1087. https://doi.org/10.3390/min12091087

AMA Style

Andrianandraina SH, Darvishi-Alamdari H, Blais J-F. Reuse of Acid Bioleachate in Bacterial Oxidation of a Refractory Gold Sulfide Concentrate. Minerals. 2022; 12(9):1087. https://doi.org/10.3390/min12091087

Chicago/Turabian Style

Andrianandraina, Sitraka Herizo, Houshang Darvishi-Alamdari, and Jean-François Blais. 2022. "Reuse of Acid Bioleachate in Bacterial Oxidation of a Refractory Gold Sulfide Concentrate" Minerals 12, no. 9: 1087. https://doi.org/10.3390/min12091087

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop