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Bioleaching of E-wastes

Arshadi, Mahdokht | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52125 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheila; Mousavi, Mohammad
  7. Abstract:
  8. This research aims to expand comprehensive information about bioleaching of different kinds of electronic waste (E-waste). The selected wastes were computer PCBs (CPCBs), mobile phone PCBs (MPPCBs), television PCBs (TVPCBs), fax machine PCBs (FPCBs), copy machine PCBs (COPCBs) and central processing units (CPUs). At the first step, a comprehensive study made on the E-waste structure. The best method for precious metal digestion analysis introduced, i.e., using aqua regia, hydrogen peroxide, hydrofluoric acid, and boric acid. The economic values of the E-wastes were as follows: CPU> MPPCBs> COPCBs> FPCBs> CPCBs> TVPCBs. Among the metals, gold attributed to the highest value distribution and palladium, copper, silver, and tin ranked the next, respectively. Bioleaching of E-waste for basic metals recovery examined using Aspergillus niger, Thiobacillus thiooxidans, and Acidithiobacillus ferrooxidans. It concluded that the bioleaching efficiency with attention to basic metals recovery and simplicity of the process is higher when A. ferrooxidans used. Consequently, bioleaching of E-waste using adapted A. ferrooxidans examined and different aspects of the process studied. The effect of daily pH adjustment on the bioleaching efficiency of E-waste studied. It confirmed the pH adjustment of the bioleaching solution is not necessary and even reduces the process efficiency. Also, the effects of the elimination of plastics were studied using the shaking table method. Based on the results using pre-treated sample was suggested. Then the D-optimal design was adopted to find the optimum combination of E-waste. The optimal combination of CPCBs plus CPU, MPPCBs, TVPCBs, COPCBs, and FPCBs to reach maximum simultaneously recovery of Cu, Fe, and Ni as the most gold inhibitor metals was determined 21.5%, 43.5%, 3%, 13.5%, and 18.5% respectively. A scale-up examined. After the definition of the optimal combination, the extraction of Cu, Fe, and Ni and important parameters including aeration, energy source, and initial pH studied in the bubble column bioreactors. At optimal condition Cu, Fe, and Ni recovered 70%, 60%, and 66% respectively in the bioreactor. The remained powder in the bioreactor used for gold bio-recovery using Chromobacterium violaceum and the separated cyanogenic bacteria from E-waste landfill. The optimum condition (including initial pH, glycine, and pulp density) for all studied cyanogenic bacteria defined. The maximum gold recovery achieved at a pulp density of 1g/l and equal to 88%. By increasing pulp density from 1 to 10g/l, the gold recovery decreased from 88% to 1/6%. One-step and two-step bioleaching examined. By using two-step bioleaching process the amount of Au recovery at a pulp density of 1 g/l from 5/4% to 32.5% and at a pulp density of 10 g/l from 3.45% to 31.38% increased. The kinetics of cyanide production was studied and all of the parameters defined. Au recovery using isolated bacteria was lower about 3.5 times rather than C. violaceum while the isolated bacteria show more viability rather than C. violaceum
  9. Keywords:
  10. Electronic Waste ; Bioleaching ; Economic Value ; Basic Materials ; Gold ; Acidithiobacillus Ferooxidans ; Chromobacterium Violaceum

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