Potential environmental risk of natural particulate cadmium and zinc in sphalerite- and smithsonite-spiked soils.

Cadmium (Cd)-bearing sphalerite and smithsonite ore particles are ubiquitous in soils near metal-mining areas. Previous studies indicate that smithsonite is more readily dissolved in acidic waters and soils than sphalerite but the mobility of Cd and zinc (Zn) derived from these ores in soils is unknown. Using microcosm incubation experiments and microscopic and spectroscopic analysis, we found that the mobility of Cd and Zn derived from smithsonite is higher than from sphalerite. The mobilization rates of Cd (16.6%) and Zn (13.7%) released from smithsonite in soils after 30-day incubation experiments were higher than those from sphalerite (Cd, ~ 1.42%; Zn, ~ 0.75%). Moreover, the percentages of Cd2+ and Zn2+ in soil pore water showed a dynamic increase in smithsonite-spiked treatments but a decrease in sphalerite-spiked treatments. HRTEM-EDX-SAED analysis further indicates the occurrence of dynamic transformation of amorphous Cd and Zn species in soil pore water to crystalline ZnS and iron oxides in sphalerite-spiked soil but crystalline ZnCO 3 nanoparticles were dynamically transformed to amorphous metal-bearing species in smithsonite-spiked soil. The opposite transformation trends in pore water of Zn ore-spiked soils provide new insights into the Cd environmental risks in soils affected by Zn mining. [Display omitted] • High mobility or bioavailability of Cd and Zn were found in SM-spiked soils. • First-order kinetic well-fitted the release of Cd and Zn derived from Zn ores. • Crystalline Zn-bearing nanoparticle dynamic transformed to amorphous colloids in SM-spike soil pore water. • Zn-bearing amorphous colloids dynamic transformed to nano-crystals in SP-spiked soil pore water. • The formation of metal-bearing nano-crystals may be frequent in the karst soil pore water. [ABSTRACT FROM AUTHOR]