Abstract
The phosphate precipitation of heavy metal induced by microorganisms plays an important role in immobilising heavy metal in soil. However, there is little knowledge about the effect of coexisting metal ions on the induction of Cu phosphate mineral and its stability. In this paper, the Cu phosphate precipitations, coexisting with Pb<sup>2+</sup> or Ca<sup>2+</sup> induced by strain LRP3, were characterised, and the stabilisation of the induced phosphate precipitates was also studied. The coexistence of Cu with Pb or Ca decreased the removal efficiency of Cu<sup>2+</sup> by 17.18% and 9.78%, respectively, indicating the competitive adsorption between cations. Strain LRP3 could induce a new phosphate mineral of CuCa<sub>10</sub>(PO<sub>4</sub>)<sub>7</sub> when coexisting with Ca and also generate the phosphate minerals of Pb(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub> and Cu<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> when coexisting with Pb. The Cu-Ca coprecipitate could enhance the stability of Cu in dilute acid solution and soil with or without a plant, whiles the Cu-Pb one showed the opposite effect. Also, the Cu-induced phosphate precipitates were relatively stable and not easy to be absorbed by Pakchoi (Brassica rapa var. chinensis). The results showed that the influence of coexisting metal ions should be considered when phosphate mineralisation technology is used to immobilise heavy metals in the environment.
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