Remediation And Utilization Of Lead-Zinc Mine Tailings Contaminated Agricultural Soils

The collapse of the tailing dam in Pb/Zn Mine of Huanjiang, Guangxi Province led to the spread of mining waste spills on the farmlands along the Huanjiang River, causing serious acid and heavy metal pollution in agricultural soils, including Pb, Cd, As and Zn. With puting forward in view of remediation and efficient utilization of polluted farmland, a field experiment was conducted on heavy metal and acid co-contaminated soils with four treatments including lime-sodium hydroxide(LS), lime-sodium hydroxide and organic fertilizer(LSO), lime-sodium hydroxide and silkworm excrement(LSSE) and CK.The effects of amendments on the growth and heavy metals(lead, cadmium, armic and zinc) accumulation characteristics of mulberry, pennisetum hydridumb, phytolacca Americana, sugarcane and solanum nigrum grown on the soil contaminated by lead/zinc mine tailings were studied. The changes of physical-chemical property of soil and content of heavy metal in soil caused by amendments were also investigated. With breeding experiment, combining laboratory inspection, the growth and heavy metal content in the edible parts of cattle feeding on Pennisetum hydridumb were investigated. Health risk assessment of heavy metals in different treatments and economic benefit analysis of different treatment for heavy metals contaminated agricultural soils were also studied.The main results of this experiment were as follows:(1) In general, lime-sodium hydroxide-silkworm excrement showed the best improvement effect on physical and chemical properties of soil. Lime-sodium hydroxide (LS), lime-sodium hydroxide-organic fertilizer (LSO), or lime-sodium hydroxide-silkworm excrement (LSSE) applied could increase soil pH and lime-sodium hydroxide showed the best improvement effect. Lime-sodium hydroxide applied reduced the concentrations of available N and available K in soil; organic fertilizer applied increased the content of organic matter, available N and available K in soil; silkworm exerement applied increased the content of organic matter, available N and available K in soil. Except mulberry planting, four plants effectively increased soil porosity and reduced soil bulk density, the effect of five plants for loosening up soil were:sugarcane/solanum nigrum>phytolacca Americana> pennisetum hydridumb> mulberry.(2) Heavy metals concentrations of contaminated farmland, including Pb, Cd, As and Zn, where mulberry, pennisetum hydridumb, phytolacca Americana, sugarcane or solanum nigrum were grown were reduced after9months in all treatments at harvest compared to those before transplanting. The phytoremediation efficiency of heavy metal contaminated soils by pennisetum hydridumb was the highest.(3) Yields of five kinds of plants were all enhanced with lime-sodium hydroxide(LS), lime-sodium hydroxide-organic fertilizer(LSO), or lime-sodium hydroxide-silkworm excrement(LSSE) applied. Application of amendments could decrease heavy metals concentrations and accumulations in the aboveground of plants at harvest, inhibit the uptake of heavy metals by plants in the aboveground. But for some plants, application of different amendments could enhance heavy metals concentrations and accumulations.(4) In general, compared with other plants, biomasses and Pb, Cd, As and Zn accumulations in aboveground part of pennisetum hydridumb are the highest. If only considering the heavy metals accumulations in aboveground part of pennisetum hydridumb, it will respectively take at least12.6,1.2and2.4years to reduce Pb,Cd and Zn content of contaminated soil in theory in order to reach the second grade standard of soil environment quality standard(GB15618-1995), with the optimum treament of CK, CK and LSSE respectively. It will take13years to reduce soil heavy metals concentrations to the safety standards for agricultural production in theory through phytoremediation of pennisetum hydridumb without amendments.(5) The levels of heavy metals in cattle muscle, heart, lungs, stomach, blood feeding on pennisetum hydridumb with or without amendments could meet the relevant standards for human consumption. Application of amendments could decrease heavy metals concentrations of pennisetum hydridumb in the aboveground part of plants, which led to the Pb, Cd and Zn concentrations in the cattle liver and kidney lower than those without amendments. But the Pb, Cd and Zn concentration in the cattle liver and kidney could not meet standards for human consumption.They were not safe for human consumption.(6) The mulberry-sericulture model is not suitable for utilization of co-contaminationed farmland because of lower economic benefits. Sugarcane, phytolacca Americana or solanum nigrum is not suitable for use in contaminated soils, because of serious health risks of heavy metals in edible parts. The model of Pennisetum hydridum-Cattle breeding is the most superior utilization model of acid and heavy metals co-contaminated agricultural soils, because of safety and economic benefits.