Pulp Density Research Articles

Hydrometallurgical recovery of manganese and nickel and isolation of tantalum from obsolete tantalum capacitor

Tantalum capacitor demand is rapidly growing, primarily from the electronic and superalloy industries. Indeed, the global tantalum market is anticipated to boost at a compound annual growth rate of around 6% over the next decade. With increasing technological advancements, electronics' obsolescence rate has also increased. The obsolete capacitors from these electronics are a rich secondary resource for recycling strategically and economically significant metals. In this article, we have developed an environment-friendly hydrometallurgical route for recovery of manganese and nickel from the tantalum capacitors. Firstly, silica-free tantalum capacitor procured after pre-processing was leached using hydrochloric acid (1–3 M) for preferred dissolution of manganese and nickel, to facilitate a tantalum-rich residue. Manganese was then selectively separated from leach liquor using solvent extraction with D2EHPA and CYANEX272, with the extraction efficiency of each reagent compared. Quantitative dissolution of both manganese (99.9%) and nickel (98.9%), with no tantalum dissolution, was witnessed under the optimized leaching condition of 3 M HCl, 50 g/l pulp density, 60 °C, and 120 min. Kinetic data for manganese and nickel in the temperature range of 30–60 °C demonstrated the leaching reaction at the surface to be the rate controlling step. D2EHPA and CYANEX272 each showed excellent selectivity for manganese under the optimized conditions. However, CYANEX272 proved to be a better extractant in light of higher extraction efficiency in single-stage extraction (∼75%), than D2EHPA (∼40%), with less organic consumption. Above 99% manganese was selectively extracted with predicted 2-stages extraction by McCabe-Thiele plot using CYANEX272 under the optimized condition.

Bioleaching Test of Polymetallic Nodule Samples from the IOM Exploration Area

The Interoceanmetal Joint Organization’s (IOM) exploration license is granted in the area located within the Clarion–Clipperton Zone of the Eastern Central Pacific. All activities related to exploration of minerals in this area are beyond the limits of national jurisdiction and come under the provision of the United Nations Convention on the Law of the Sea and related regulations. The geological survey, which was the subject of the exploration, focused on the polymetallic nodule deposits. Other activities covered the tests of nodule processing, including alternative methods of metal extraction. This article describes the methodology of the bioleaching process and provides a summary of the initial results of the bioleaching test, applied to the samples of polymetallic nodules taken from the H22 exploration block of the IOM exploration area. The bioleaching efficiency under different pulp density conditions was studied. The enrichment of heterotrophic Mn-reducing microorganisms was prepared as the leaching medium. Bioleaching of the samples took place with different sample weights in order to determine the maximum possible extraction yield and the highest concentration of elements obtained in the leachate. During the bioleaching, the media were also exchanged to achieve maximum polymetallic nodule decomposition with regular addition of nutrients for heterotrophic Mn-reducing bacteria. The bioleaching efficiency of the polymetallic nodules increased to 100% (without Cu) when the pulp density was reduced to 0.1% (w/v). The discontinuous bioleaching and washing process recovered 55% Mn, 36% Ni, 15% Co, 27% Zn, and 38% Cu when the pulp density was increased to 10% (w/v). To achieve total Mn, Cu, Zn, Co, and Ni recovery from the polymetallic nodules, an intermittent bioleaching with about 25 changes of 60% of the medium was required when the pulp density was increased to 10% (w/v). Bioleaching has the potential to be used as an environmentally friendly alternative to other commonly used options for leaching and processing.

An HGA-LSTM-Based Intelligent Model for Ore Pulp Density in the Hydrometallurgical Process.

This study focused on the intelligent model for ore pulp density in the hydrometallurgical process. However, owing to the limitations of existing instruments and devices, the feed ore pulp density of thickener, a key hydrometallurgical equipment, cannot be accurately measured online. Therefore, aiming at the problem of accurately measuring the feed ore pulp density, we proposed a new intelligent model based on the long short-term memory (LSTM) and hybrid genetic algorithm (HGA). Specifically, the HGA refers to a novel optimization search algorithm model that can optimize the hyperparameters and improve the modeling performance of the LSTM. Finally, the proposed intelligent model was successfully applied to an actual thickener case in China. The intelligent model prediction results demonstrated that the hybrid model outperformed other models and satisfied the measurement accuracy requirements in the factory well.

Separation and Recovery of Cu from Industrial Dust via a Solvometallurgical Process

In this study, a solvometallurgical process for the recovery of Cu from industrial dust by leaching with a lixiviant comprising hydrochloric acid (HCl) and ethylene glycol followed by extraction with trioctylphosphine oxide (TOPO) was developed. Copper, Ni, Mg, and Al contained in the dust were efficiently dissolved by using HCl in ethylene glycol, leaving most of the Ag in the residue. The parameters (concentration of the lixivant, reaction temperature, pulp density) that affect leaching efficiency were extensively investigated and optimized. TOPO was used to selectively extract Cu over other metal ions (Ni, Mg, Al, and Ag) from the obtained leachate. The Cu extraction mechanism was investigated by using the slope method, and 0.1 mol/L sulfuric acid was used to strip Cu from the Cu-loaded TOPO. McCabe–Thiele plots for Cu extraction and stripping were constructed to determine the number of counter-current stages along with the volumetric flow ratio of the two phases. Counter-current Cu extraction and stripping simulation tests were carried out to confirm its feasibility. Finally, a flow diagram of the proposed process for separation and recovery of Cu from industrial dust is provided.

Selective recovery and intensification of Mn from spent LiMn2O4 using sulfuric acid as lixiviant and Na-D2EHPA as extractant

ABSTRACT Despite the rising demand for lithium-ion batteries and their widespread acceptance, recycling and repurposing end-of-life lithium-ion battery materials is still a work in progress. This will help mitigate the dependence on raw materials and risks of shortage while promoting a circular economy. The present work addresses a hydrometallurgical process to recover Mn from spent LiMn2O4 using sulphuric acid as a lixiviant and Na-D2EHPA as extractant. Effects of various leaching parameters have been studied and the pregnant leach solution has been generated using 1 mol/L H2SO4 with 6% H2O2 at a pulp density of 10 g/L, maintaining the temperature at 30°C at 450 rpm for 1 hour which contained 2.52 g/L Mn and 0.545 g/L of Li. The PLS was subjected to separation using solvent extraction method taking 70% saponified di-(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant. The McCabe-Thiele plot suggested two theoretical stages at O:A ratio of 1:1 using 0.3 mol/L Na-D2EHPA with 99.94% extraction of Mn and 10.2% co-extraction of Li. The co-extracted lithium was removed by scrubbing with MnSO4 solution. The loaded organic containing 2.574 g/L Mn was stripped using 10% H2SO4 at two stages at O: A ratio of 1.5:1 and enriched the concentration of manganese 1.5 times in the stripped solution.

Recovery of surface-plated metals from lead frame scrap using selective leaching and solvent extraction

The selective leaching of surface-plated metals from lead frame scrap followed by metal separation and enrichment through solvent extraction has been investigated. The leaching of lead frame scrap using H2SO4 solution under non-oxidizing and oxidizing conditions could efficiently and selectively dissolve Ni, leaving majority of Cu-substrate in the leach residue for further processing. The leaching carried out in a 1.0 M H2SO4 solution at 400 rpm agitation speed, 90 °C temperature and 15 g/L pulp density yielded a Ni leaching efficiency of 98.6% for 240 min (non-oxidative), but required only 60 min to reach the Ni efficiency of 96.4% while supplying 1.0 L/min O2 (oxidative). For both leaching systems, Cu dissolution was found to be <7% only without any dissolution of precious metals contained in the scrap. The kinetic study showed that the Ni leaching under non-oxidizing conditions proceeded by a single rate-controlling step following film diffusion model with activation energy of 12.6 kJ/mol in the temperature range 50–90 °C.The Ni leaching in oxidative system was however, controlled by a mixed control model comprising film diffusion and chemical reaction with the activation energy of 40.0 kJ/mol in the same temperature range. These results were corroborated by SEM analysis of the leach residue. Subsequently, leach liquor obtained from the oxidative leaching (0.84 g/L Cu2+ and 0.32 g/L Ni2+) was subjected to solvent extraction using LIX 84-I. Based on the extraction data, a two-stage counter-current extraction at A/O ratio = 10/1 was required using 20% LIX 84-I to quantitatively extract and enrich Cu2+ from the solutions (equilibrium pH 2.5). The stripping of Cu-loaded organic phase indicated that a three-stage counter-current stripping using 200 g/L H2SO4 at O/A ratio of 5/1 was required. Nickel(II) from the copper free aqueous solution was extracted and enriched using 20% LIX 84-I at an A/O ratio of 5/1, and was stripped from the loaded organic phase using 20 g/L H2SO4 at O/A ratio of 5/1. The hydrometallurgical route of selective leaching-SX results in not only Cu- and Ni-rich solutions suitable for recovery of final products, but also Ni-free lead frame scrap for further processing by smelting. Finally, a flowsheet has been proposed for the total recycling of lead frame scrap.

Sequential biologically assisted extraction of Cu and Zn from printed circuit boards (PCB)

ABSTRACT The increased production and use of electrical and electronic equipment leads to obsolescence and disposal problems, necessitating materials recovery and recycling. This paper reports results on metal bioleaching from printed circuit boards (PCBs) using chemolithotrophic bacteria isolated at different sulphide ore biotopes in Armenia. Different ways of generating lixiviants were investigated, namely using combination of Acidithiobacillus ferrooxidans 61 and Acidithiobacillus thiooxidans SO-1 bacteria generating biogenic Fe2(SO4)3 and biogenic H2SO4. The sequence between these leaching agents permitted design of a 2-step process based on acidolysis and redoxolysis to leach non-ferrous metals from PCBs. To compare the efficiency of the sequential bioleaching of PCBs, several experimental runs were realised under the six modes at 10% pulp density. The flasks-based tests have witnessed almost complete recovery of Cu with the rest of the metals reaching extraction degree above 80%.

Effective purification of graphite via low pulp density flotation-low temperature alkali roasting-acid leaching route: From laboratory-scale to pilot-scale

A typical flake graphite concentrate sampled from a graphite flotation plant was used to prepare high purity graphite. The carbon content of the concentrate was 85.6%, and silicate and iron-containing minerals were found principally in the concentrate. High-grade graphite concentrate with a carbon content of 95% was obtained in the flotation process with feed pulp of 5% solids by weight after regrinding by a low-speed ball milling system. A small amount of the flotation reagents such as caustic soda, water glass, kerosene, and pine oil were added. The resulting flotation concentrate was mixed with alkali and roasted at 500 °C for 90 min. During the alkali roasting, the silicate mineral was converted into the water- and acid-soluble materials. Afterward, the soluble materials and iron-containing minerals were dissolved by acid leaching. As a result, a product with a carbon content of 99.82% was prepared. According to the calculation results of Gibbs energy, the reactions between impurities and chemicals in alkali roasting and acid leaching processes were spontaneous. The purification route was very effective for high purity graphite production and has been successfully applied in the pilot-scale experiment.

A classical modelling of abandoned mine tailings' bioleaching by an autochthonous microbial culture

The aim of this study was to study and model the bioleaching of abandoned mine tailings at different pulp densities 1–20% w/v by using an autochthonous mesophilic microbial culture. Because of the importance of the ferrous-iron oxidation as sub-process on the bioleaching of sulphide mineral ores, the ferrous-iron oxidation process by the autochthonous microbial culture was studied at different ferrous-iron concentrations. A mathematical model fitted to the experimental results and the main kinetic and stoichiometric parameters were determined, being the most relevant the maximum ferrous-iron oxidation rate 5.1 (mmol Fe2+/mmol C·h) and the biomass yield, 0.01 mmol C/mmol Fe2+, values very similar to that of mixed cultured dominated by Leptospirillum strains. This autochthonous culture was used in the bioleaching experiment carried out at different pulp densities, obtaining a maximum metal recovery in the tests carried out at 1% w/v, recovering a 90% of Cd, 60% of Zn, 30% of Cu, 25% Fe and 6% of Pb. Finally, the different leaching mechanisms were modelled by using the pyrite as ore model obtaining a bioleaching rate of 0.316 mmol Fe2+/(L·h) for the direct mechanisms and a bioleaching rate for the indirect and cooperative leaching mechanisms of 0.055 Fe2+/(L·h).

Desulfurization of natural gas condensate using polyethylene glycol and water intercalated activated γ-bauxite

Three different active γ-bauxite were developed from a low-grade raw boehmite ore, as a cheap and efficient adsorbent for the desulfurization of gas condensates. The first adsorbent (RBa) was developed directly through a two-stage thermochemical activation (thermal activation process followed by an acid treatment) of the boehmite ore. The other two adsorbents (PBa and WBa) were initially intercalated with polyethylene glycol (PEG) solution or water, respectively, at the optimum temperature and pressure followed by thermochemical activation to modify the pore size and active surface area. The process parameters such as pulp density and leaching time were optimized using response surface methodology (RSM) based on central composite design (CCD).Comparing the performance of prepared adsorbents to remove sulfur-containing compounds from natural gas condensate indicated the superior sulfur removal efficiency of PBa compared to WBa and non-intercalated adsorbents. Using PBa, the sulfur content was significantly reduced from 2821 ppm to <35 ppm. Characterization of the developed adsorbents indicated that after thermal activation, the pore size of the non-intercalated adsorbent was significantly reduced, which negatively affects its desulfurization efficiency. Nevertheless, the pore diameter of PBa was maintained similar to that of raw bauxite while its surface area was approximately 12-fold larger, which confirms the successful role of PEG as a lattice expansion element, improving its desulfurization efficiency.

Optimization of Gold Dissolution Parameters in Acidified Thiourea Leaching Solution with Hydrogen Peroxide as an Oxidant: Implications of Roasting Pretreatment Technology

The nature of gold (Au) ore deposits plays an essential role in determining the best gold recovery method as an alternative to cyanidation, considering environmental concerns. Thiourea (Tu) leaching of gold is an alternative lixiviant for treating sulfide gold ores and concentrates. The present study investigated the leaching behavior of Au from sulfide gold ore concentrates obtained from the Cripple Creek site (Newmont operated mine) using acidified thiourea solution. The concentrates containing pyrite, K-feldspar, quartz, and gypsum as major minerals were roasted before leaching to break down complex sulfides and improve the gold’s leachability. Parameters investigated include the leaching time (1–7 h), temperature (20–60 °C), pulp density (20–60 g/L), and thiourea concentration (20–60 g/L) to determine optimum conditions for Au dissolution. Hydrogen peroxide (H2O2) was used as an oxidizing agent and sulfuric acid (H2SO4) to maintain an acidic environment during the leaching process. The highest Au dissolution percentage of 96.2 was obtained after 6 h of leaching with 40 g/L thiourea at 60 °C, pH 1, and pulp density of 20 g/L. Based on the results presented in this work, the dissolution of gold with thiourea in an acidic solution would be a potential alternative to the traditional cyanide process, with the increase in understanding of the green leaching of Au from sulfide gold ores.

Bioconversion and quantification of humic substances from low rank coals using indigenous fungal isolates

The major portion of coals around the world belongs to lignitic origin, and burning of these Low Rank Coals (LRCs) not only produces energy, but also release harmful gases into the environment. On the other hand, coal is a mega source of fossilized carbon compounds that can be utilized in diverse range of carbon/organic industries. Biosolubilization is one of the safest and economical way to consume these LRCs for the harvest of humic and fulvic acids for industrial applications. Present studies deal with solubilization of coal samples from five different mines of Punjab, Pakistan by indigenously isolated fungus. From a number of indigenously isolated fungal isolates, an isolate NF-2 was selected based on its solubilization potential on solid Sabouraud medium. The intensity of coal biosolubilization was found maximum for coal sample B-1 (59%) and lowest for sample B-26 (17.2%) with 5% (w/v) pulp density at 28 ± 2 °C. Humification index value (A4/A6) for biosolubilized products of coal sample B-1 was found 6.18 which was much higher than the A4/A6 value (4.27) of commercially available standard humic acid. Biosolubilized products from coal sample B-1 was found maximum with 8681 mg/L humic acid concentration as determined by standard curve method. FTIR and FE-SEM analyses of sample B-1 treated with NF-2 confirmed the structural break down and solubilization of coal. Molecular identification of fungal isolate NF-2 showed 100% similarity to Aspergillus flavus. This work paves the way to utilize lignitic coals for the environment friendly and low-cost production of humic acids by fungal biosolubilization as an alternate to chemical methods.

Two-Stage Oxidative Leaching of Low-Grade Copper-Zinc Sulfide Concentrate.

Bioleaching may be effectively used to extract nonferrous metals from sulfide ores and concentrates. At the same time, some minerals are refractory and their bioleaching rate is often comparatively low that does not allow the required metal extraction rate to be achieved. In the present work, we studied the two-stage process, which included stages of biological and chemical leaching, to improve copper extraction from low grade Cu–Zn sulfide concentrate containing chalcopyrite, tennantite, pyrite, and sphalerite. Bioleaching was conducted in the continuous mode in three laboratory scale reactors connected in series. The pulp density was 10% and the residence time was 7 days. The temperature was 40 °C in the 1st reactor and 50 °C in the 2nd and 3rd reactors. Bioleaching allowed the extraction of 29.5 and 78% of Cu and Zn, respectively. The solid bioleach residue obtained was then treated for additional Cu and Zn recovery using high temperature leaching at 90 °C for 25 h. The liquid phase of the bioleaching pulp contained Fe3+ ions, which is the strong oxidant, and the leach solution was supplemented with NaCl. In the presence of the maximal NaCl concentration (1 M), Cu and Zn extraction reached 48 and 84%. Thus, two-stage leaching may allow to increase bioleaching efficiency and may be used to improve the bioleaching rate of refractory minerals, such as chalcopyrite.

Enhanced metal bioleaching mechanisms of extracellular polymeric substance for obsolete LiNixCoyMn1-x-yO2 at high pulp density.

Harmful chemicals present in electric vehicle Li-ion batteries (EV LIBs) can limit the pulp density of bioleaching processes using Acidithiobacillus sp. to 1.0% (w/v) or lower. The strong enhancing mechanisms of extracellular polymeric substances (EPS) on the bioleaching of metals from spent EV LIBs at high pulp density (4% w/v) were studied using bio-chemical, spectroscopic, surface structure imaging and bioleaching kinetic methods. Results demonstrated that the added EPS significantly improved bioleaching efficiency of Ni, Co and Mn improved by 42%, 40% and 44%, respectively. EPS addition boosted the growth of cells under adverse conditions to produce more biogenic H+ while Fe3+ and Fe2+ were adsorbed by the biopolymer. This increased Li extraction by acid dissolution and concentrated the Fe3+/Fe2+ cycle via non-contact mechanisms for the subsequent contact bioleaching of Ni, CO and Mn at the EV LIB-bacteria interface. During the leaching process, added EPS improved adhesion of the bacterial cells to the EV LIBs, and the resultant strong interfacial reactions promoted bioleaching of the target metals. Hence, a combination of non-contact and contact mechanisms initiated by the addition of EPS enhanced the bioleaching of spent EV LIBs at high pulp density.

Feasibility of direct conversion of copper present in waste printed circuit boards to oxidation-resistant materials employing eco-benign iron(III) sulfate and ascorbic acid

This study presents the feasibility of an eco-benign, practical hydrometallurgical process for the recovery of Cu(0) as an oxidation-resistant material from waste printed circuit boards (WPCBs) with minimum chemical consumption. In leaching, metals were leached using Fe2(SO4)3, and 98.4 ± 1.5% Cu(II) was achieved under optimum conditions (0.1 M Fe2(SO4)3, 10 g/L pulp density, 25 °C, and 6 h). Then, 95.8 ± 0.3% Cu(0) was selectively recovered from multi-metal containing acidic leachate by a cementation method under the optimum conditions (0.3 M ascorbic acid, 70 °C, and 4 h). The as-recovered Cu(0) was characterized via quantitative and qualitative analyses and compared with a commercial Cu(0) as a reference material. As results, the high purity Cu(0) (99.2% Cu and 0.44% Ag) was recovered, and it was confirmed that the as-recovered Cu(0) can be used as an oxidation-resistant material owing to a trace amount of Ag. Finally, the economic feasibility of the developed process was evaluated based on the experimental results and the price of oxidation-resistant Cu in the e-commerce market ($10–50/kg). The minimum selling price of as-recovered Cu(0) can be estimated to be $26.16 per kg, which is a reasonable market price for oxidation-resistant Cu(0).

Green extraction of nickel and valuable metals from pyrrhotite samples with different crystallographic structures through acidophilic bioleaching.

Nowadays, due to the strategic status of nickel in the global market, utilizing its disregarded resources like low-grade nickel containing pyrrhotite is of significant importance. A comprehensive set of experiments and analyses were performed to determine the bioleaching capability and mechanism for nickel extraction from hexagonal and monoclinic pyrrhotite. Over 95% Ni extraction was achieved from the hexagonal pyrrhotite sample. Ni extraction from the monoclinic sample reached its maximum value of 67% and 90% at 3% pulp density, with mixed mesophilic and moderately thermophilic cultures, respectively. Characterization analyses indicated that jarosite and elemental sulfur formation in mixed mesophilic bioleaching reduced the samples' bio-oxidation rate and metal dissolution. The kinetics study revealed that the controlling step in thermophilic bioleaching is the chemical reaction; however, the mixed control model was best fitted on mesophilic data. Electrochemistry studies confirmed bioleaching results and indicated that monoclinic pyrrhotite's oxidation rate under the operating conditions is faster than hexagonal pyrrhotite, and the temperature positively correlates with the oxidation rate. Toxicity assessment analysis showed that the final residues of both bioleached samples could be considered environmentally safe.

Bulk flotation followed by selective leaching with biogenic ferric iron is a promising solution for eco-friendly processing of complex sulfidic ores.

The development of cost-effective environmentally friendly technologies is of current importance for the intensification of metal recovery. Here, we propose a new direction in the use of a two-step process for the treatment of complex sulfidic ores. In the first step, ore flotation allows the obtainment of a bulk copper-zinc concentrate and low-toxicity waste. In the second step, zinc is selectively extracted by chemical leaching with a biogenic ferric iron solution, while copper is accumulated in the leach residue. Importantly, the efficiency of this step depends on the chemical and mineralogical composition of polymetallic concentrates. Four samples of the copper-zinc sulfide concentrate with various contents of copper and zinc have been leached in multiple cycles at 80°C, 10% of pulp density, and pH 1.3-1.5. The leaching of the concentrate that contained 14.7% of copper and 5.0% of zinc for three leaching cycles (total duration, 5.75h) allowed the obtainment of a leach residue containing 15.3 and 0.14% of copper and zinc, respectively. At the same time, the leaching of another concentrate that contained 19.2% of copper and 2.64% of zinc after one leaching cycle (total duration, 0.67h) led to copper and zinc contents of 19.1 and 0.72%, respectively, in the leach residue. Therefore, the treatment of only two concentrates allowed the obtainment of high-grade copper concentrates containing low amounts of zinc. Ferric iron, the oxidant of sulfide minerals, was fully regenerated in leachate within 30-35h at 40°C using an acidophilic microbial community dominated by Leptospirillum ferriphilum, Sulfobacillus spp., and Ferroplasma acidiphilum. The loss of copper and zinc in solid waste of the bioregeneration did not exceed 1.0% and 1.8%, respectively. The proposed flowsheet of bulk concentrate processing has several important advantages over conventional technologies, including short duration of leaching, formation of low-toxicity solid waste, and pyrometallurgical processing of only high-grade copper concentrates. This approach can be a promising solution for the efficient processing of polymetallic bulk concentrates.

Understanding the Entrainment Behavior of Gangue Minerals in Flake Graphite Flotation

Flotation is one of the most used methods to upgrade natural graphite resources. However, the efficiency is usually decreased due to the entrainment of undesirable fine gangue minerals. In this work, the impact of different factors such as particle size, pulp density, and flotation reagent on the entrainment of mica and quartz in a flake graphite flotation was studied. The single gangue mineral flotation results showed increased gangue entrainment when reducing the particle size of gangue minerals and increasing the pulp density. Moreover, the flotation of artificial mixtures indicated enhanced entrainment of mica and quartz in the presence of graphite particles. The collector and frother also strongly affect gangue entrainment by modifying the structure and stability of the froth. Kerosene, which has a prominent deforming feature, can reduce gangue entrainment more effectively than diesel.

Green recovery of cerium and strontium from gold mine tailings using an adapted acidophilic bacterium in one-step bioleaching approach

BackgroundEnormous amounts of gold mine tailings (GMT) are produced as a result of mineral activities, but these mine tailings produced from previous ore processing still contain significant amounts of elements (e.g. strontium (Sr)) and rare earth elements (REEs) such as cerium (Ce). In this study, extraction of Ce and Sr from GMT using an adapted sulfur oxidizers acidophilic strain for developing a one-step bioleaching was performed for the first time. MethodsDetermination of the optimal conditions by response surface methodology (RSM), for maximizing Ce and Sr recovery, was carried out using influential factors of initial sulfur concentration, pH and pulp density. Significant findingsThe optimal values of pH, pulp density and initial sulfur concentration were 1.8, 2% (w v-1) and 0.55% (w v-1), respectively. The highest sulfate production was obtained in initial sulfur concentration of 0.5% (w v-1). In addition, among the various inhibition kinetic models, Tessier inhibition kinetic model was the most suitable based on the experimental data. In conclusion, the kinetic study of the process indicated that a high recovery of 75.8% of Ce and 86.4% of Sr was achieved from GMT under optimal conditions, where the chemical reaction was revealed to be the rate controlling step. Bioleaching of GMT by A. thiooxidans is a promising technology to reduce the environmental hazards of these wastes. The results showed that GMT can be a source of supply of Ce and Sr.

Scrap computer keyboards a sustainable resource for silver (Ag) and low density oil (L D Oil)

Most neglected part of the scrap computers are the keyboards, which are generally incinerated by the informal recycling sectors creating environmental pollution and leads to the wastage of precious metallic contents present in it. Present paper is focused on a novel chemical processing technique developed to recover silver (Ag) as value added product and low density oil (L D Oil) from the computer keyboards. Initially, scrap keyboards were manually dismantled to separate Mylar sheets and the same were pyrolysed at 300 °C for 2 h to recover L D Oil. The obtained pyrolysed Mylar sheets was further crushed, milled and homogenized to reduce particle size (−100 mesh). The crushed sample was leached using 2 M HNO3 at 60 °C in mixing time of 20 min and pulp density of 100 g/L to achieve maximum dissolution of Ag. The leaching kinetics for Ag dissolution well fitted with chemical reaction control dense constant size cylindrical particles, 1-(1-X)1/2 = kct. The obtained leach liquor was put to cementation process using metallic copper (Cu). Almost 99% of Ag gets cemented as Ag powder in 15 min at a constant solution temperature of 60 °C and pH 1.1. The developed bench scale process has application orientation to the industry after piloting the process.