Removal of heavy metals by calcium stripping in a fluidized bed

Abstract

This research was to study the removal efficiency of heavy metals from industrial wastewater by using of a fluidized sand bed as a "calcium and metal" stripper. in operation, the metal-bearing wastewater was pumped through the sand bed with a proper dosing of calcium and alkalinity to effect the precipitation and coating of calcium and metal carbonates on the sand surface. The fluidized sand bed provided a heterogeneous system to allow rapid nucleation/crystallization on sand surface and result in effective coplating (deposition) of calcium carbonate, metal carbonates and possibly some metal hydroxides on the sand surface through lattice compatibility and crystal sweeping/enmeshment. It had been found that for metal-spiked tap water with an ititial metal concentration of 22 mg/L and an operating pH of 8.5~9.0, the removal efficiency of soluble metal ions was over 99%. The total metal (untiltered) removal efficiency for copper, chromium , nickel and zinc were approximately 81%, 77%, 90% and 74%, respectively. The escaped metals existed primarily as finely-divided metal precipitates which resulted from "discrete precipitation" and failed to coat on the sand surface. The cations in the coated material contain 51% as metals (including 7% as Cu,19% as Cr,14% as Ni and 11% as Zn) and 49% as calcium. However, it was also found that as the operation extended longer, the percentage of metals on the coated material would increase continuously while that of calcium would decrease.

Keywords: Heavy metal removal, calcium stripping, calcium carbonate, metal carbonates, metal hydroxides, crystallization, deposition, co-precipitation.

Date of Award	1996
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology