Remediation of lead (Pb(II)) wastewater through recovery of lead carbonate in a fluidized-bed homogeneous crystallization (FBHC) system

This work demonstrated the removal of lead (Pb) from aqueous solution using fluidized-bed crystallization (FBC, using silica sand as seeds) and fluidized-bed homogeneous crystallization (FBHC, without seeds) systems. Synthetic lead wastewater with concentrations of 10, 40 and 200 ppm were treated. The results thus obtained indicated that effluent pH was an essential parameter in determining the efficiency of FBC and FBHC. A comparison between theoretical solubility and residual Pb in effluents revealed that FBHC in the predictable metastable region of pH 6.5–8.5 guaranteed 99% Pb removal and a crystallization ratio of 95% (CR%). XRD analysis suggested that the lead carbonate of FBHC products comprised either a cerussite (PbCO3) or a hydrocerussite (Pb3(CO3)2(OH)2) phase, depending on pH. FBHC was proven to be effective in remediating lead wastewater under optimal hydraulic conditions (initial molar ratio of [Na2CO3]/[Pb] > 1.2, upflow velocity = 25–35 m h−1 and pHe = 7.2 ± 0.4), which were all similar to those in FBC. The cross-section loading (L, kg m−2 L−1) depended on the input Pb level; L was controlled at 0.15 kg m−2 h−1 for treating 10 ppm-Pb and was increased to 5.73 kg m−2 h−1 for 40 and 200 ppm-Pb, optimizing the FBHC and FBC processes. Without the addition of seed materials, FBHC recovered purer lead carbonate than did FBC.