Characterization of biological iron sulfide composites and its application in the treatment of cadmium-contaminated wastewater.

A strain of sulfate reducing bacteria, which could generate biological iron sulfide composites, was applied for Cd (II) removal from wastewater. The influence of biological iron sulfide composites dosage, initial pH and temperature on the rate of Cd (II) removal from wastewater by biological iron sulfide composites were investigated. The microscopic morphological characteristics and elemental composition changes of the biological iron sulfide before and after treatment was compared, using scanning electron microscopy and energy-dispersive spectrometry, then the mechanism of Cd (II) removal was explored. The results showed that Cd (II) reduction rate increased with increase in dosage of biological iron sulfide composites and initial temperature. At 25 degrees C, pH 4.0, with dosage of sulfide and cadmium ions molar equal to 99.93% Cd (II) was removed from cadmium wastewater (100 mg l(-1)), and the residual concentration of cadmium reached Chinese Integrated Wastewater Discharge Standard (GB8978-1996). The present study revealed that bio- precipitation of FeS, the main component of biological iron sulfide composites, played leading role in the process of Cd (II) reduction. Therefore, it is prospective to apply biological iron sulfide composites in the emergency treatment of cadmium-contaminated wastewater.