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Li J.,Central South University | Li J.,Hunan University | Zhou Z.,Shenzhen Hazardous Waste Treatment Station Co. | Yang T.,Central South University | Chen L.,Central South University
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology)

Fluoride in waste acid was removed by precipitation process with waste residue and dust containing lead oxide. The thermodynamics of H+-F--H2O and Pb2-F--H2O systems were analyzed. The distribution diagram of lead and fluoride species, E-log [F-] diagram and solubility curve of lead fluoride diagram at 25°C were drawn. The relationship among the total lead concentration ([Pb]T) /fluoride concentration ([F]T) and free lead concentration ([Pb2+]) and pH were obtained. The results show that lead and fluoride mainly exist as free ions in the solution with pH between 4-6. When pH exceeds 7, free lead ion concentration in the solution is reduced significantly, resulting in the reduction of fluoride removal efficiency. Fluoride exists mostly in the form of HF when solution pH is lower than 4. The optimum conditions for fluoride removal are as follows: temperature is 25°C, pH is 6, and total lead concentration is 0.01 mol/L. Under the condition, the total fluoride mass concentration can be decreased to about 40 mg/L. This method can provide a new way in waste acid treating process for metallurgical works. Source

Chen X.,Central South University | Zhao X.,Jinchuan Nickel and Cobalt Research and Design Institute | Chu G.,Central South University | Zhou Z.,Shenzhen Hazardous Waste Treatment Station Co. | And 2 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology)

Pretreatment with dilute nitric acid-leaching with sodium sulfite process was adopted to recover silver from silver separating residue. The effects of the concentration of reagents of pretreatment process, concentration of reagents, solid to liquid ratio (S/L ratio), temperature, time, pH of leaching process were investigated. The results show that the silver leaching rate can achieve over 95% when leaching conditions are as follows: pretreatment with 2% dilute nitric acid, with concentration of sodium sulfite being about 200 g/L, pH=8, S/L ratio being 1:8, 2 h reaction time, at 30 °C. This process has the advantage of easy operation, low energy consumption, and being environmentally friendly. Therefore, it is significant in energy saving and environmental protection of silver separating residue. Source

Wu L.,Tianjin University of Technology | Liu Z.,Tianjin University of Technology | Qin S.,Tianjin University of Technology | Cheng L.,Shenzhen Hazardous Waste Treatment Station Co.
Chinese Journal of Environmental Engineering

Biological deodorization of hydrogen sulfide was studied through the reduction of ferric sulfate which were bio-oxidized from ferrous sulfate by Acidithiobacillus thiooxidans in a laboratory-scale trickle-bed bioreactors system. The operating parameters of bioreactor and H2S absorption tower were the aeration amount of 150 L/h, the absorbent liguid Fe3+ concentration of 0.121~0.143 mol/L, the absorption liquid flow of 0.3 L/h, the gas flow of 100 L/h. Under the optimal operating conditions, the removal rate of H2S achieved about 95% and 91% at the inlet concentrations of 2.28 mg/L and 9.11 mg/L in the intake gas, respectively. The system tended to be relatively stable after the system had continuously run for 200 min. Source

Xue L.,Tianjin University of Technology | Qin S.,Tianjin University of Technology | Liu Z.,Tianjin University of Technology | Wu L.,Shenzhen Hazardous Waste Treatment Station Co. | And 2 more authors.
Huagong Xuebao/CIESC Journal

Acidithiobacillus ferroxidans was used to oxidize Fe2+ into Fe3+ in the ferrisulfas liquor, and then dissolved Fe3+ was reduced by H2S, achieving both reclamation of the liquor and removal of H2S. The key factor for the removal efficiency of this treatment system was high concentration of dissolved Fe3+. However, when NH4 + and K+ were excessive, most portions of dissolved Fe3+ would be transferred into Jarosite. The nitrogen source was optimized to obtain high concentration of Fe3+ by controlling its ingredients and concentrations. It showed that (NH4)2HPO4 could replace (NH4)2SO4 to be the nitrogen source and its concentration in 0.33-1 g·L-1 was a suitable range for cell growth of Acidithiobacillus ferroxidans. At 1 g·L-1, the bacterial growth did not exhibit obvious lag period; average oxidation rate of Fe2+ was 0.221-0.229 g·(L·h)-1, dissolved Fe3+ increased to 7.62-7.72 g·L-1, and precipitation was 1.17 g·L-1. Therefore, the optimal concentration of (NH4)2HPO4 was 1 g·L-1. In order to reduce cost, the concentration was lowered 0.33 g·L-1. This technique not only maintained the Fe2+ oxidative activity of Acidithiobacillus ferroxidans but also effectively increased dissolved Fe3+ produced during bacterial culture process, providing scientific optimization basis for removal of H2S by the ferrisulfas liquor. © All Rights Reserved. Source

Qing X.,South China Institute of Environmental Sciences | Han J.-L.,South China Institute of Environmental Sciences | Wen Y.-S.,Shenzhen Hazardous Waste Treatment Station Co.
Huanjing Kexue/Environmental Science

Concentrations of 17 PCDD/Fs congeners in spent etching solution and its copper salt recycling products were determined by the high resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS). The PCDD/F concentrations and corresponding WHO-TEQ (toxic equivalent quantity) values were in the range of 0-3 460 pg·L-1 (mean=616 pg·L-1) and 0-246 pg·L-1 (mean=42.9 pg·L-1), respectively, in the spent etching solution, and 1.08-24.6 ng·kg-1 (mean=8.83 ng·kg-1) and 0.112-0.715 ng·kg-1 (mean=0.338 ng·kg-1), respectively, in the copper salt products. The established purification treatment technique could remove most of the PCDD/Fs in the etching solution. Of the copper products, higher PCDD/F concentrations were detected in industrial products than in feed grade and plating grade products. Similar distribution characteristics were found for PCDD/Fs in all copper salt products as the followings: (1) PCDFs were more abundant than PCDDs, (2) high chlorinated congeners were more abundant than low chlorinated congeners, except for 2, 3, 7, 8 -TCDF in the copper sulfate products. Source

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