Nano sized CdS and PbS particles: Preparation by coupling of biological reduction and chemical precipitation mediated with EDTA

High-purity nano CdS and PbS particles were synthesized using a coupling reaction of biological reduction and chemical precipitation mediated with EDTA referred as CRBRCP-EDTA process. The results showed that the concentration increase of C ^d2+, between 0.0125 and 0.037 5 mol'L ^-1, enhanced the bioreduction of S0 ₄ ^2- and CdS bioproduction. But the high concentration of Cd ²⁺, 0.05 mol'L ^-1, inhibited the biological activity of sulfate reduction bacteria (SRB) and reduced CdS production. In the reaction of anaerobic reduction, slightly soluble PbS0 ₄ sedimentation gradually transformed into insoluble PbS sedimentation, leading to nano PbS production. The diameter of CdS solid spheres is 10-20 nm for primary particles and around 400 nm for secondary particles. When polyacrylamide (PAM) was incorporated in the process, the distribution of secondary particles diameter of CdS were more uniform. The secondary particles diameter of PbS solid spheres is about 40 nm, and it did not change when PAM incorporated, but the morphology transformed from sphere to cube. The bioproduction of metal-sulfide using CRBRCP-EDTA process can be extended to other metals, leading to a bright prospect for wider application.