High Pulp Density Research Articles

Effect of metal sulfide pulp density on gene expression of electron transporters in Acidithiobacillus sp. FJ2.

In Acidithiobacillus ferrooxidans, one of the most important bioleaching bacterial species, the proteins encoded by the rus operon are involved in the electron transfer from Fe2+ to O2. To obtain further knowledge about the mechanism(s) involved in the adaptive responses of the bacteria to growth on the different uranium ore pulp densities, we analyzed the expression of the four genes from the rus operon by real-time PCR, when Acidithiobacillus sp. FJ2 was grown in the presence of different uranium concentrations. The uranium bioleaching results showed the inhibitory effects of the metal pulp densities on the oxidation activity of the bacteria which can affect Eh, pH, Fe oxidation and uranium extractions. Gene expression analysis indicated that Acidithiobacillus sp. FJ2 tries to survive in the stress with increasing in the expression levels of cyc2, cyc1, rus and coxB, but the metal toxicity has a negative effect on the gene expression in different pulp densities. These results indicated that Acidithiobacillus sp. FJ2 could leach the uranium even in high pulp density (50%) by modulation in rus operon gene responses.

Study of cut point density and process performance of Floatex density separator in fine coal cleaning

ABSTRACTAdvanced gravity separation of a high-ash (36%) semi-coking coal in a Floatex density separator (FDS) is investigated. The influence of the operating variables on the separation features has been identified. It is established that a higher bed pressure and a higher teeter water flow rate enhance the mass yield of the clean coal albeit with a poorer grade. A higher bed pressure reduces the bed voidage leading to a higher cut point density. Although bed voidage is reduced due to higher teeter water rate, the hydraulic transport increases significantly. A higher pulp density and a higher feed rate introduce severe hindered settling conditions leading to an increase in the cut point density. This results in a poorer product grade with a higher yield. The optimum condition for 23% product ash in a single-stage operation is identified. The yield at the optimum condition is found to be 64.3% which is close to the theoretical maximum for this coal. The dependence of the cut point density as well as Ecart probable (Ep) value on the operating variables is quantified. A specific gravity of separation of below 1.8 and an Ep value of around 0.15 is achievable under controlled operation of the FDS.

Maximization of organic acids production by Aspergillus niger in a bubble column bioreactor for V and Ni recovery enhancement from power plant residual ash in spent-medium bioleaching experiments

Spent-medium bioleaching of V and Ni from a power plant residual ash (PPR ash) was conducted using organic acids produced by Aspergillus niger. The production of organic acids in a bubble column bioreactor was optimized through selecting three most influencing factors. Under optimum condition of aeration rate of 762.5(ml/min), sucrose concentration of 101.9(g/l) and inoculum size of 40(ml/l), respectively 17,185, 4539, 1042 and 502(ppm) of oxalic, gluconic, citric and malic acids were produced. Leaching experiments were carried out using biogenic produced organic acids under leaching environment temperature of 60°C and rotary shaking speed of 135rpm, with various pulp densities of 1, 2, 3, 5, 7 and 9(%w/v). The results showed that biogenic produced organic acids leached V much more efficiently than Ni so that even at high pulp density of 9(%w/v), 83% of V was recovered while Ni recovery yield was 30%.

A New Heterotrophic Strain for Bioleaching of Low Grade Complex Copper Ore

A new heterotrophic strain, named Providencia sp. JAT-1, was isolated and used in bioleaching of low-grade complex copper ore. The strain uses sodium citrate as a carbon source and urea as a nitrogen source to produce ammonia. The optimal growth condition of the strain is 30 °C, initial pH 8, sodium citrate 10 g/L and urea 20 g/L, under which the cell density and ammonia concentration in the medium reached a maximum of 4.83 × 108 cells/mL and 14 g/L, respectively. Ammonia produced by the strain is used as the main lixiviant in bioleaching. Bioleaching results revealed that higher strain growth led to a higher copper recovery, while higher pulp density will cause a greater inhibitory effect on strain growth and ammonia production. The copper extraction reached the highest value of 54.5% at the pulp density of 1%. Malachite, chrysocolla and chalcocite are easy to leach out in this bioleaching system while chalcopyrite is difficult. Results of comparative leaching experiments show that bioleaching using JAT-1 is superior to ammonia leaching at the same condition. The metabolites produced by the strain other than ammonia are also involved in bioleaching.

Mineralogy, Geochemistry and Stable Isotope Studies of the Dopolan Bauxite Deposit, Zagros Mountain, Iran

A new heterotrophic strain, named Providencia sp. JAT-1, was isolated and used in bioleaching of low-grade complex copper ore. The strain uses sodium citrate as a carbon source and urea as a nitrogen source to produce ammonia. The optimal growth condition of the strain is 30 C, initial pH 8, sodium citrate 10 g/L and urea 20 g/L, under which the cell density and ammonia concentration in the medium reached a maximum of 4.83 × 108 cells/mL and 14 g/L, respectively. Ammonia produced by the strain is used as the main lixiviant in bioleaching. Bioleaching results revealed that higher strain growth led to a higher copper recovery, while higher pulp density will cause a greater inhibitory effect on strain growth and ammonia production. The copper extraction reached the highest value of 54.5% at the pulp density of 1%. Malachite, chrysocolla and chalcocite are easy to leach out in this bioleaching system while chalcopyrite is difficult. Results of comparative leaching experiments show that bioleaching using JAT-1 is superior to ammonia leaching at the same condition. The metabolites produced by the strain other than ammonia are also involved in bioleaching.

Application of response surface methodology to optimize uranium biological leaching at high pulp density

Abstract The aim of the present study was to carry out uranium bioleaching via optimization of the leaching process using response surface methodology. For this purpose, the native Acidithiobacillus sp. was adapted to different pulp densities following optimization process carried out at a high pulp density. Response surface methodology based on Box-Behnken design was used to optimize the uranium bioleaching. The effects of six key parameters on the bioleaching efficiency were investigated. The process was modeled with mathematical equation, including not only first and second order terms, but also with probable interaction effects between each pair of factors.The results showed that the extraction efficiency of uranium dropped from 100% at pulp densities of 2.5, 5, 7.5 and 10% to 68% at 12.5% of pulp density. Using RSM, the optimum conditions for uranium bioleaching (12.5% (w/v)) were identified as pH = 1.96, temperature = 30.90 ℃, stirring speed = 158 rpm, 15.7% inoculum, FeSO4 · 7H2O concentration at 13.83 g/L and (NH4)2SO4 concentration at 3.22 g/L which achieved 83% of uranium extraction efficiency. The results of uranium bioleaching experiment using optimized parameter showed 81% uranium extraction during 15 d. The obtained results reveal that using RSM is reliable and appropriate for optimization of parameters involved in the uranium bioleaching process.

Metallic ions catalysis for improving bioleaching yield of Zn and Mn from spent Zn-Mn batteries at high pulp density of 10%

Bioleaching of spent batteries was often conducted at pulp density of 1.0% or lower. In this work, metallic ions catalytic bioleaching was used for release Zn and Mn from spent ZMBs at 10% of pulp density. The results showed only Cu2+ improved mobilization of Zn and Mn from the spent batteries among tested four metallic ions. When Cu2+ content increased from 0 to 0.8g/L, the maximum release efficiency elevated from 47.7% to 62.5% for Zn and from 30.9% to 62.4% for Mn, respectively. The Cu2+ catalysis boosted bioleaching of resistant hetaerolite through forming a possible intermediate CuMn2O4 which was subject to be attacked by Fe3+ based on a cycle of Fe3+/Fe2+. However, poor growth of cells, formation of KFe3(SO4)2(OH)6 and its possible blockage between cells and energy matters destroyed the cycle of Fe3+/Fe2+, stopping bioleaching of hetaerolite. The chemical reaction controlled model fitted best for describing Cu2+ catalytic bioleaching of spent ZMBs.

Bioleaching of copper, nickel and cobalt from the low grade sulfidic tailing of Golgohar Iron Mine, Iran

This study was conducted to establish the possible application of bioleaching to recover valuable metals from the sulfidic tailing of Golgohar Iron Mine (Kerman, Iran). Shake flask leaching experiments were carried out in the presence of a mixed culture of moderately thermopilic microorganisms at a stirring rate of 150rpm and a temperature of 45°C, with the addition of yeast extract (%0.02 (w/w). The influence of bacterial inoculation, pH, nutrient medium type and pulp density on the recovery of copper, nickel and cobalt from the tailing was investigated. The results showed that 55.0% of copper, 98.2% of nickel and 59.5% of cobalt could be extracted from the tailing through the bioleaching process after 30days at 5% (w/v) pulp density. The recovery of valuable metals from the tailing in the presence of microorganisms was approximately three times higher than that in the un-inoculated leaching experiment under similar conditions. It was also found that the recovery of copper at the initial pH of 1.2 was 17% higher than that at the pH of 1.8, while nickel and cobalt recoveries were 37% and 23% more at the pH of 1.8, respectively. It was also revealed that the recoveries of valuable metals were approximately similar in both 9K and Norris nutrient media. Moreover, the results showed that in both nutrient media, copper recovery at the higher pulp density was significantly higher than that at the lower pulp density; this was mainly attributed to the lower redox potential. On the other hand, nickel and cobalt recoveries were higher at the lower pulp density, probably due to the higher redox potential values. A two-stage bioleaching process in which the redox potential is controlled at a low level in the primary reactors, followed by the secondary reactors with a high redox potential is supposed to achieve the maximum recovery of valuable metals.

Development of two-step process for enhanced biorecovery of Cu–Zn–Ni from computer printed circuit boards

Metal pollution due to the huge electronic waste (E-waste) accumulation is widespread across the globe. Extraction of copper, zinc and nickel from computer printed circuit boards (c-PCB) with a two-step bleaching process using ferric sulphate generated by Leptospirillum ferriphilum dominated consortium and the factors influencing the process were investigated in the present study. The studied factors with 10 g/L pulp density showed that pH 2.0 was optimum which resulted in 87.50-97.80% Cu-Zn-Ni extraction. Pre-treatment of PCB powder with acidified distilled water and NaCl solution showed 3.80-7.98% increase in metal extraction corresponding to 94.08% Cu, 99.80% Zn and 97.99% Ni extraction. Particle size of 75 μm for Cu and Zn while 1680 μm for Ni showed 2-folds increase in metal extraction, giving 97.35-99.80% Cu-Zn-Ni extraction in 2-6 days of reaction time. Whereas; 2.76-3.12 folds increase in Cu and Zn extraction was observed with the addition of 0.1% chelating agents. When the studies were carried out with high pulp density, ferric iron concentration of 16.57 g/L was found to be optimum for metal extraction from 75 g/L c-PCB and c-PCB addition in multiple installments resulted in 8.81-26.35% increase in metal extraction compared to single addition. The studied factors can be implemented for the scale-up aimed at faster recovery of multimetals from E-waste and thereby providing a secondary source of metal in an eco-friendly manner.

Effect of mixed moderately thermophilic adaptation on leachability and mechanism of high arsenic gold concentrate in an airlift bioreactor

A refractory gold concentrate with 19% arsenic was treated by a mixed moderately thermophiles in an airlift bioreactor through an adaptation protocol. The moderately thermophiles could respond well to 20% (w/v) pulp density with less than 10% loss of productivity, and resist arsenic up to 15 g/L. There were a lot of jarosite, arsenolite and sulfur, but not scorodite and ferric arsenate in the bioleached residue. Jarosite passivation and lower sulfur-oxidizing activity of the cells due to the toxicity of the high concentrations of soluble arsenic and iron ions at low pH value should mainly response for the incomplete extraction at high pulp density. The initial bacterial community did not change in nature except for new found P aeruginosa ANSC, but sulfur-oxidizing microorganisms have been dominant microorganisms after a long time of adaptation. Pseudomonas aeruginosa originating from the gold concentrate should be closely relative to the metabolism of the organic matters contained in the refractory gold concentrate.

Continuous Bioleaching of Chalcopyritic Concentrate at High Pulp Density

The main objective of the present study was to investigate the continuous bioleaching of chalcopyrite concentrate at a high pulp density by moderate thermophilic microorganisms. Using a flotation concentrate containing 46% chalcopyrite and 23% pyrite, bioleaching tests were carried out at a high pulp density (15%) and temperature of 47°C using a setup consisting of three continuous stirred tank bioreactors in series. A two-level full factorial design of experiments was used to assess the effects of residence time, particle size and acidity of the leaching solution on the copper recovery. From the results of these tests, we concluded that under the best process conditions (d80 = 30 μm, T = 47°C, and acidity of 130 kg/ton) more than 54% of copper was extracted from the concentrate after 7 days. Also, the concentration of copper in the final solution was higher than 20 g/L.

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrateat 45-47 degrees C and pH 1.8-2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the micioorganisms from thie experimental and aboriginal communities during oxidation of sulfide ore flotation concentrate at 47 degrees C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus strains (the most active sulfur oxidizers) and Sulfobacillus thermotolerans strains (active oxidizers of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrates at high pulp density (S:L = 1:4).

Process controls for improving bioleaching performance of both Li and Co from spent lithium ion batteries at high pulp density and its thermodynamics and kinetics exploration

Release of Co and Li from spent lithium ion batteries (LIBs) by bioleaching has attracted growing attentions. However, the pulp density was only 1% or lower, meaning that a huge quantity of media was required for bioleaching. In this work, bioleaching behavior of the spent LIBs at pulp densities ranging from 1% to 4% was investigated and process controls to improve bioleaching performance at pulp density of 2% were explored. The results showed that the pulp density exerted a considerable influence on leaching performance of Co and Li. The bioleaching efficiency decreased respectively from 52% to 10% for Co and from 80% to 37% for Li when pulp density rose from 1% to 4%. However, the maximum extraction efficiency of 89% for Li and 72% for Co was obtained at pulp density of 2% by process controls. Bioleaching of the spent LIBs has much greater potential to occur than traditional chemical leaching based on thermodynamics analysis. The product layer diffusion model described best bioleaching behavior of Co and Li.

Leaching kinetics of enargite in alkaline sodium sulphide solutions

Leaching of enargite samples containing approximately 12% As, 0.5% Sb and 39% Cu was studied in alkaline sulphide solutions containing sodium hydroxide and sodium sulphide. Kinetic parameters studied included temperature, particle size, reagent concentration, agitation rate and stoichiometry in high pulp density experiments. The extraction of arsenic was chemical reaction controlled with an activation energy of 74kJmol−1, indicating the importance of temperature on the process. The relative contributions of total initial sulphide and hydroxide concentrations on leaching kinetics were determined and a new rate equation was developedrAs=−dAsdt=k'As2.37S2−1.83OH−3.31,kgt−1h−1where k′ depends on system activation energy and can be predicted from this parameter (it had a value of 1.63×10−3 in this work). This rate equation was validated against data presented in other similar studies of enargite leaching. It is demonstrated that the hydroxide ion plays a direct role in the leaching reaction, rather than simply ensuring adequate sulphide speciation. Copper, iron, zinc, and silver were not extracted during the leaching procedure. Through chemical analysis, X-ray diffraction and scanning electron microscopy leach residues were characterised. Residues contained copper–sulphur compounds such as digenite, bornite and sodium copper sulphide (NaCu5S3).

Anglesite (PbSO4) leaching in citrate solutions

The thermodynamics and kinetics of anglesite leaching in citrate solutions was studied at room temperature. Solution pH and pulp density were found to have a pronounced effect on lead extraction. Thermodynamic analysis suggested that the lead solubility in citrate is maximized at pH values near 7, which was corroborated through leaching tests. The limited solubility was found to severely hamper the leaching rate at high pulp densities. A shrinking particle model with solubility control was used to describe the results.

The application of diffusion–reaction mixed model to assess the best experimental conditions for bark chemical activation to improve copper(II) ions adsorption

Natural sorbents have been thoroughly assessed to determine their adsorption capabilities to remove pollutants from industrial wastewaters. Among them, pine bark has demonstrated potential for carrying out the removal of contaminants, particularly heavy metals, at the level of traces present in dissolved state. Nevertheless, to move towards the wastewater treatment implementation at large scale, the handling and processing requirements of pine bark to optimise the adsorption of heavy metals must be fully assessed. This research study presents a new mathematical model to evaluate the impact of acid pre-treatment of pine bark on heavy metals adsorption at different pine bark-aqueous solution pulp densities. A diffusion–reaction mixed model was developed and applied to the case study of copper(II) adsorption onto pine bark. The low binding energy inferred from analysing the adsorption isotherms suggested that a diffusive mechanism is governing the whole process. The mixed diffusion–reaction kinetic model indicated that the activation increases the rate at which metal ions are adsorbed, but it reduces the maximum achievable adsorption which in turn restricts its usefulness to relatively high pulp densities (above 10 g/L). The latter constitutes the first step towards optimising the use of bark pine for treating wastewater polluted with heavy metals and for establishing rules for scaling-up the process.

A Moderately Thermophilic Mixed Microbial Culture for Bioleaching of Chalcopyrite Concentrate at High Pulp Density

Three kinds of samples (acid mine drainage, coal mine wastewater, and thermal spring) derived from different sites were collected in China. Thereafter, these samples were combined and then inoculated into a basal salts solution in which different substrates (ferrous sulfate, elemental sulfur, and chalcopyrite) served as energy sources. After that, the mixed cultures growing on different substrates were pooled equally, resulting in a final mixed culture. After being adapted to gradually increasing pulp densities of chalcopyrite concentrate by serial subculturing for more than 2 years, the final culture was able to efficiently leach the chalcopyrite at a pulp density of 20% (wt/vol). At that pulp density, the culture extracted 60.4% of copper from the chalcopyrite in 25 days. The bacterial and archaeal diversities during adaptation were analyzed by denaturing gradient gel electrophoresis and constructing clone libraries of the 16S rRNA gene. The results show that the culture consisted mainly of four species, including Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus acidophilus, and Ferroplasma thermophilum, before adapting to a pulp density of 4%. However, L. ferriphilum could not be detected when the pulp density was greater than 4%. Real-time quantitative PCR was employed to monitor the microbial dynamics during bioleaching at a pulp density of 20%. The results show that A. caldus was the predominant species in the initial stage, while S. acidophilus rather than A. caldus became the predominant species in the middle stage. F. thermophilum accounted for the greatest proportion in the final stage.

Arsenopyrite bioleaching by Acidithiobacillus ferrooxidans in a rotating-drum reactor

A rotating-drum reactor with a gas-sparger of microfiltration ceramic membrane was used for arsenopyrite bioleaching by Acidithiobacillus ferrooxidans. The gas mass transport performance could be improved by adjusting the aeration rate and drum rotation speed, and high bioactivity of bacterial strains could be maintained at high pulp densities. Arsenopyrite bioleaching showed that higher pulp density could be allowed in the rotating-drum reactor, which was favorable to the reactor used in the bioleaching of sulfide minerals.

Adsorption and zeta potential studies relevant to hematite ore reverse froth flotation

Reverse froth flotation is the most commonly used concentration method for iron ores, where the quartz gangue is floated, while the iron oxides are depressed by starches. in this paper, the mechanisms related to iron ore anionic reverse flotation are investigated by flotation, electrokinetic and high pulp density (20% solids) adsorption studies in alkaline medium using sodium oleate as the model collector. distribution diagrams of silicate and oleate species are employed to interpret the effects of ph on the electrokinetic and adsorption studies. the flotation experimental results showed that with ca2+ as activator, quartz responded to flotation well, whereas hematite does not. the changes in zeta potential for quartz are attributed to the hydroxylation of the quartz surface at different ph values and collector concentrations. coated starch can shift the zeta potential of hematite particles to less positive values and increase its potential differences from quartz and support quartz-hematite separation during flotation. adsorption results indicated that sodium oleate adsorbs onto the mineral surfaces to form surfactant multilayers due to the lateral interaction between hydrocarbon chains. adsorption kinetics studies showed that calcium ions can change the collector adsorption kinetics curve on quartz from first order to second order. minerals & metallurgical processing, 2012, vol. 29, no. 3, pp. 148-155. an official publication of the society for mining, metallurgy, and exploration, inc.

Analysis of reasons for decline of bioleaching efficiency of spent Zn–Mn batteries at high pulp densities and exploration measure for improving performance

The reasons for decline of bioleaching efficiency of Zn and Mn from spent batteries at high pulp densities were analyzed; the measures for improving bioleaching efficiency were investigated. The results showed that extraction efficiency of Zn dropped from 100% at 1% of pulp density to 29.9% at 8% of pulp density, with Mn from 94% to only 2.5%. It was almost the linear reduction of the activity of the sulfur-oxidizing bacteria with increase of pulp density that witnessed declined bioleaching efficiency of Zn; it was the complete inactivation of the iron-oxidizing bacteria at 2% of pulp density or higher that witnessed declined bioleaching dose of Mn. By means of reducing initial pH value of leaching media, increasing concentration of energy matters and exogenous acid adjustment of media during bioleaching, the maximum extraction efficiency of almost 100% for Zn and 89% for Mn at 4% of pulp density was attained, respectively.