| Development in industry has caused more environmental problems, chromium pollution received much attention. The physical and chemical methods for chromium remediation consume a lot of energy, and causes secondary contamination due to the addition of chemical regents in the process. The bio-remediation method with its low-cost and environment-benign character being using to treat chromium slags have been paid more attention. This paper explored the effect of mineralization characteristics to solidify chromium slags on the harmless treating based on the bio-mineralization of Microbacterium sp.GM-1.Firstly, Microbacterium sp.GM-1 was breed to examine its urease activity and characteristic of urea-resistance and Cr(VI)-resistance. The ammonia generated from urea using GM-1 in flat experiments was detected by phenol red(indicator), which proves the urease activity of Microbacterium sp.GM-1.The urea-resistance of Microbacterium sp.GM-1 was studied in the flask-shaking test with four concentrations of Urea ranging from 20 to 80 g/L(20 g/L, 40 g/L, 60 g/L, 80 g/L) being added into the NB culture medium. The growth curve indicated that the environment of the culture is very suitable to Microbacterium sp.GM-1 until it increases to the concentration of 60g/L.The Cr(VI)-resistance character was studied with the different concentrations of Cr(VI) ions(0 mg/L, 100 mg/L, 200 mg/L and 120 mg/L, 140 mg/L, 160 mg/L, 180mg/L) being added into the medium. The test showed that Microbacterium sp.GM-1 can tolerate to the concentration of up to 120 mg/L Cr(VI).Secondly, a certain amount of white precipitation detected as CaCO3 using XRD was observed in the shaking flasks with addition of the different concentrations of Ni2+(0 μmol/L, 100 μmol/L, 200 μmol/L) ions before the test and the equal amounts of CaCl2 solution two days later.It is found that Ni2+using as catalyst promotes the mineralization process of GM-1. To investigate the optimum bio-mineralization, Four factors, Ni2+, urea, pH and time, were selected to design the orthogonal test. The influence of the factors ranks as urea﹥time﹥pH﹥Ni2+was gotten basing on the results of the range analysis. The optimal parameter combination were followed as: 50 μmol/L of Ni2+, 60 μmol/L of urea, 10 of pH and 96 hours of culture time.Thirdly, Microbacterium sp.GM-1 was added in solidification process to study the effect of bio-mineralization on chromium waste forms. Chromium waste forms(2cm×2cm×2cm) were prepared with chromium, sand and soil in the proportion of8:1:1(m/m/m), which were mixed with Microbacterium sp.GM-1(1:7(v/m)) and incubated in room temperature for 28 d. Nutrient solution was overliad on the specimens at an interval of 7d. There were control experiment without Microbacterium sp.GM-1.The physical-chemical characteristic of chromium waste forms was tested and analyzed,containing Thermo-Gravity(TG), chemical speciation, compress strength and leaching toxicity. The specimen lost some weight in the range of 600℃ to 700℃ in TG process which was attributed to the thermal decomposition calcium carbonate induced by bio-mineralization.The stable structure of Cr(VI)-CaCO3 generated with priority in chromium waste forms according to the chemical speciation analysis was concluded as the main reason for the higher compress strength(0.6341 MPa) and lower leaching toxicity(balance leaching 0.1269 mg/g, dynamic leaching<2 mg) of chromium waste forms.Lastly, the most appropriate proportion of chromium slag forms was tested at different raw material ratios(8:2:1,8:2:0.5,8:1:1,8:1:0.5). Combined with analysis of compress strength and leaching toxicity, 8:1:1 was demonstrated to be mostly feasible under laboratory conditions. |
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