Effect Of Rock Phosphate Powder On Heavy Metals Contaminated Soil In Mining Area

Mining exploration and melting cause multi-metal pollution in mine andsurrounding areas, which directly threaten the quality safety of agricultural products,human health and ecological security. Therefore, it’s important to study remediationtechniques for heavy metals contaminated soil in these areas.Chemical remediation immobilizes heavy metals and reduces the bioavailability incontaminated soils by chemical amendments and is a promising practical method.Phosphorous materials have been widely accepted as efficient additives for heavy metalscontaminated soil. There are many phosphorous mine resources in China, can be appliedbroadly. It has been reported that the particle size of additives and the amount haveeffects on heavy metals remediation.Two kinds of concentration in combination with four different sizes of phosphate,<101.43、<71.12、<36.83and <4.26μm, were added to mining soil as amendments. Fromthe batch soil column incubation experiment to the pot experiment of maize and ryegrass,a series of work was conducted to study the effect of phosphate amendments additive onthe fraction transformation, bioavailability and the phytoextaction efficiency of heavymetals by hyperaccmulator. Some key results were summarized as follows:1. Phosphate additive increased pH in Pb, Zn, Cu and Cd contaminated acid soil, andsignificantly reduced Pb, Zn and Cu in acid extractable fraction. As the incubation timeincreased, it was shown that acid extractable fraction decreased. Compared withnon-additive treatment, Pb in acid extractable fraction respectively decreased by4.3%~11.6%、4.3%~10.2%and5.2%~12.9%after1month,2months and3months.Amending multiple heavy metals contaminated soil with phosphate rock powders cansignificantly reduce heavy metals phytoavailability and bioaccessibility.2. Due to the complicated interaction of Pb, Zn, Cu and Cd, it’s more of difficulty tofind a proper solution to heavy metals immobilization in soil. Among these four heavymetals, Pb, Zn, Cu and Cd, phosphate rock powder has more effect on Pb, Zn and Cu, especially on Pb. Phosphate rock powder can be widely applied into practice as multipleheavy metals amendment, particularly for high Pb and Zn concentration contaminatedmining soil.3.5%concentration addition of phosphate rock powder generally showed moreefficiency in increasing the biomass of maize and ryegrass, reducing Pb, Zn and Cu acidextractable fraction that meant heavy metals moved from high available speciation tostable speciation, which resulted in effectively less Pb, Zn and Cu accumulation in maizeand ryegrass.4. No obvious difference has been found between different particle sizes ofphosphate rock powder treatments at the same addition concentration,2.5%or5%, whichwas probably attributed to the particle sizes ranging within micron scales couldn’t lead tosignificant attribution difference. Above all,5%addition of phosphate rock powder sized<4.26μm has the best effect on heavy metals immobilization and plants accumulationreduction.