Analysis of reasons for decline of bioleaching efficiency of spent Zn-Mn batteries at high pulp densities and exploration measure for improving performance.
ABSTRACT 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.
- SourceAvailable from: Ata AkcilRecycling Industry. 03/2014;
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ABSTRACT: The present study evaluated the potential of Bacillus megaterium as a cyanogenic bacterium to produce cyanide for solubilization of platinum and rhenium from a spent refinery catalyst. Response surface methodology was applied to study the effects and interaction between two main effective parameters including initial glycine concentration and pulp density. Maximum Pt and Re recovery was obtained 15.7% and 98%, respectively, under optimum conditions of 12.8g/l initial glycine concentration and 4% (w/v) pulp density after 7days. Increasing the free cyanide concentration to 3.6mg/l, varying the pH from 6.7 to 9, and increasing the dissolved oxygen from 2 to 5mg/l demonstrated the growth characteristics of B. megaterium during bioleaching process. The modified shrinking core model was used to determine the rate limiting step of the process. It was found that diffusion through the product layer is the rate controlling step.Bioresource Technology 08/2014; 171C:401-409. · 5.04 Impact Factor
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ABSTRACT: In this study, spent batteries were selected from municipal waste for bioleaching and extraction of their heavy metals. The bioleaching of nickel, cadmium, and cobalt from Ni–Cd and NiMH batteries was done using Acidithiobacillus ferrooxidans, a resistant strain used for bioleaching. The adaptation process was successful and the solid-to-liquid ratio reached 10 g/L (battery powder weight/volume of medium). A Box–Behnken design of response surface methodology (RSM) was used to investigate the effects of initial pH, powder size, and initial Fe3+ concentration on the percentage of metals recovered. The proposed statistical method was used to accurately evaluate the interactions of the factors and their effects on the recovery efficiency of nickel, cadmium and cobalt during bioleaching. Under the specified conditions, up to 99% recovery was observed for each metal, confirming that A. ferrooxidans is an effective toxin resistant microorganism for bio-recovery of heavy metals. Decreasing the initial pH and particle size and increasing the initial Fe3+ concentration led to maximum recovery for nickel and cobalt; while the optimum condition for cadmium was different for Ni and Co. To maximize simultaneous extraction of three metals, the optimum value for initial pH, particle size and initial Fe3+ concentration were obtained 1, 62 μm and 9.7 g/L, respectively. Under these conditions, the recoveries predicted by the software (Design Expert version 7.1.4) were 85.6% for Ni, 66.1% for Cd, and 90.6% for Co. These results were confirmed using a verification experiment at optimum condition, which calculated 87%, 67%, and 93.7% for Ni, Cd and Co, respectively. Due to the distinct chemical characteristics of Cd in contrast with Ni and Co, its recovery in the optimal condition for simultaneous recovery was decreased; in the other words; Cd recovery was higher when it was the sole target for extraction.Separation and Purification Technology 08/2014; 132:309–316. · 2.89 Impact Factor