Gang Zou

Fluidized-bed denitrification of mining water tolerates high nickel concentrations

This study revealed that fluidized-bed denitrifying cultures tolerated soluble Ni concentrations up to 500 mg/L at 7-8 and 22°C. From 10 to 40 mg/L of feed Ni, denitrification resulted in complete nitrate and nitrite removal. The concomitant reduction of 30 mg/L of sulfate produced 10 mg/L of sulfide that precipitated nickel, resulting in soluble effluent Ni below 22 mg/L. At this stage, Dechloromonas species were the dominant denitrifying bacteria. From 60 to 500 mg/L of feed Ni, nickel remained in solution due to the inhibition of sulfate reduction. At soluble 60 mg/L of Ni, denitrification was partially inhibited prior to recover after 34 days of enrichment by other Ni-tolerant species (including Delftia, Zoogloea and Azospira) that supported Dechloromonas. Subsequently, the FBR cultures completely removed nitrate even at 500 mg/L of Ni. Visual Minteq speciation model predicted the formation of NiS, NiCO3 and Ni3(PO4)2, whilst only Ni3(PO4)2 was detected by XRD.

Effect of arsenic on nitrification of simulated mining water

Mining and mineral processing of gold-bearing ores often release arsenic to the environment. Ammonium is released when N-based explosives or cyanide are used. Nitrification of simulated As-rich mining waters was investigated in batch bioassays using nitrifying cultures enriched in a fluidized-bed reactor (FBR). Nitrification was maintained at 100mg AsTOT/L. In batch assays, ammonium was totally oxidized by the FBR enrichment in 48 h. As(III) oxidation to As(V) occurred during the first 3h attenuating arsenic toxicity to nitrification. At 150 and 200mg AsTOT/L, nitrification was inhibited by 25%. Candidatus Nitrospira defluvii and other nitrifying species mainly colonized the FBR. In conclusion, the FBR enriched cultures of municipal activated sludge origins tolerated high As concentrations making nitrification a potent process for mining water treatment.

Impact of heavy metals on denitrification of simulated mining wastewaters

Thespreading of nitrogenous compounds into the environment is a common challenge duringmining industries. Typical explosives used in mining are N-based compoundswhich lead to nitrogen contamination of groundwater and water bodies. In goldextraction, cyanide used as lixiviant is also another source of nitrogen pollution.The present work aims to investigate the effect of heavy metals ondenitrification using batch bioassays. Cu, Ni, Co and Fe influence ondenitrification process was studied at pH 7.0. Below the soluble concentrationof 62 mg/L, Ni did not inhibit denitrification, whereas denitrification wasrepressed at soluble Ni concentration above 62 mg/L. At 122 mg/L of soluble Ni,50% inhibition of denitrification was observed. Below soluble concentration of86 mg/L, Co exerted no inhibitory effect on nitrate removal but moderatelydecreased the denitrification rate. Cu slowed denitrification down resulting in40% of nitrate removal averagely at the soluble concentration below 1 mg/L. Onthe contrary, Fe supplementationresulted in iron oxidation and soluble Fe concentrations ranging from 0.4-1.6mg/L that stimulated denitrification. Thepresent work indicates that denitrification can tolerate heavy metals and canbe suitable for acid mine drainage remediation.

Column Bioleaching of Low Grade Copper Sulfide Ore at Extreme Conditions for Most Mineral Processing Bacteria

This study is prompted by the high leaching efficiency of Zijinshan copper bio-heap leaching industrial plant. Bioleaching columns with 100 mm diameter and 1 m height were used to investigate copper bioleaching at different operating conditions. Elevated temperature, high total iron concentration and high acidity significantly increased copper leaching rate as determined by solution and residue assays. At 60 °C with 50 g/L iron (initial Fe3+/Fe2+ gram ratio 2.5), pH 1.0 and no aeration, copper extraction was achieved 90% after 60 days. However, at 30°C, 5 g/L total Fe, pH 1.5 and no aeration, copper extraction reached 80% and 85% after 90 and 200 days, respectively. Real-time PCR assay showed that only 105 cells/ml and 2×105 cells/g are in solution and on the ore surface at the condition of 60 °C 50 g/L iron and pH 1.0, respectively. In addition, a similar leaching rate was observed in the tests with and without inoculation. The column without inoculation was directly irrigated with acid mine drainage (AMD). Our results indicate high copper leaching efficiency at extreme conditions for mineral oxidizing bacteria. Inoculation and aeration are not necessary in Zijinshan copper mine bio-heap leaching process.

Dissolution of Pyrite Particles by Chemical Oxidation and Bioleaching

Dissolution of pyrite by chemical oxidation and bioleaching were studied with using short-term batch experiments. The results show that the rate of oxidative dissolution of pyrite increases with the increasing concentration of ferric in ferric sulfate solutions. With the corresponding in the bioleaching, the leaching rate of pyrite is markedly affected by the Eh of the solution. The ferric/ferrous ratio controls the relative rate of the oxidation reactions involved in the process. Additionally, the leaching rate of pyrite is controlled by the pH. The phase analysis of products indicated that S2- 2oxidation can produce S0 and SO2- 4under these conditions. On the basis of predecessors and using these species，the simplest expected oxidation mechanism is S2O2- 3regarded as the intermediate mechanism during the oxidation process.