A new process for removing metal contamination from wastewater has been developed. This work applied carbonate salts as a precipitant for homogeneously producing metal carbonate crystal without seed materials from synthetic wastewater using a fluidized bed homogeneous crystallizer (FBHC).
In calcium removal experiment, The optimum pH of about 10 to 11. The calcium removal efficiency could achieve more than 99 % and crystallization ratio could achieve more than 93% for various initial calcium concentration (50 – 150 ppm). FBHC technology is suitable to deal with the cross-section loading of zinc wastewater below 5.5 Kg/m2hr for pH 10.8 – 11.2. The XRD analysis indicated that the calcium salt crystallization product was consisted of two calcium carbonate (CaCO3) phases, the calcite, the aragonite, and the calcium oxide (CaO). The surface morphology of SEM analysis revealed that calcium carbonate particles (around 0.8 mm) were formed by the aggregation of fine crystal (around 5 μm) layer by layer
In a zinc removal experiment, at an optimum pH was about 9 to 10 zinc removal efficiency could achieve more than 99.9% and crystallization ratio could achieve more than 95% for various zinc concentration (50 – 150 ppm). FBHC technology could deal with the cross-section loading of zinc wastewater below 2.3 Kg/m2hr for pH 9.6 – 9.8. The XRD analysis showed that the FBHC product was a mixed phase of Smithsonite (ZnCO3) and Hydrozincite (Zn5(OH)6(CO3)2). The surface morphology of SEM analysis revealed that zinc carbonate particles (around 0.5 mm) were formed by the aggregation of fine crystal (around 4 μm).
In mixed compound, zinc and calcium removal was held in two series FBHC because of the different optimum pH for zinc and calcium removal. The initial concentrations of zinc was 300 ppm and that of calcium was 75 and 750 ppm. Both, zinc and calcium removal could achieve above 99%. The crystallization ratio achieved 98% for zinc and 96% for calcium.
In tap water softening process, under pH above 10.5, calcium removal achieved more than 90%. The low magnesium ions in tap water significantly affect the softening results.

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