| Heavy metal pollution in farmland soil is a high environmental and toxicological concern.Pollution of heavy metal had posed a serious threat to ecological environmental quality,food safety and economic sustainable development. Remediation of heavy metal contaminated soil is a sensitive and thorny issue in environmental pollution control and it is also a current outstanding environmental problem to be solved. In this paper, a pot experiment and an indoor cultivation experiment was carried out to study the effect of phosphate rock and rice straw on lead passivation and soil basic properties. Field experiments were also conducted in Taolin lead-zinc mine area, located in Zhongfang town, Linxiang city, Hunan province. The field experiment conducted was aimed at fixating soil heavy metals by using the phosphate rock. The main results were as follows:1) The application of phosphate rock improved Chinese cabbage leaf chlorophyll,biomass and reduced lead content and the accumulation of lead in Chinese cabbage. In pot experiment, the treatment of activated phosphate rock containing a concentration of0.12 g/kg P2O5 improved Chinese cabbage chlorophyll value more than 33%, compared with the contrast. While the treatment of the same amount of raw phosphate rock only improved 10%. After 45 natural long-term, the biomass of a Chinese cabbage of control treatments was only 1.48 g. The application of phosphate rock and activated phosphate rock relieved the lead stress and reduced the lead poisoning, and promoted the biomass of Chinese cabbage. The biomass of a Chinese cabbage increased to over 2 g. The biomass of a Chinese cabbage in the high amount of activated phosphate rock treatment was highest, more than 5 g. Lead concentrations of Chinese cabbage in control treatment was up to 17.18 mg/kg, and lead cumulated amount was 25.3 ug/plant. For the treatments of low level of activated phosphate rock and high level activated phosphate rock, the contents of Chinese cabbage lead were reduced to 4.96 mg/kg and 2.78 mg/kg, and the lead accumulation was decreased by 25% and 25%, respectively.2) Adding phosphate rock and rice straw significantly increased the soil p H,Olsen-P, exchangeable calcium and cation exchange capacity, and the treatment ofactivated phosphate rock was better than the raw phosphate rock. In pot experiment,adding phosphate rock and rice straw raised soil p H up to 0.48 units, increased content of Olsen-P in soil by 1.06 to 8.21 mg/kg, increased exchangeable calcium by 0.14 to 0.49cmol/kg, increased cation exchange capacity of the soil by 0.23 to 1.81 cmol/kg. While in cultivation experiment, adding phosphate rock and rotten rice straw raised soil p H up to0.28, increased the content of Olsen-P in soil by 0.11 to 9.16 mg/kg, increased exchangeable calcium in soil by 0.04 to 0.72 cmol/kg, increased cation exchange capacity of the soil by 0.22 to 1.44 cmol/kg. The soil p H value of flooded treatment was higher than the treatment of keeping 70% of the field water holding capacity. The former was higher by 0.14 than the later, on average. The treatment of adding rotten rice straw had a higher content of Olsen-P than the treatment of not adding rotten rice straw,increased by 0.36 mg/kg, on average. Content of Olsen-P of flooded treatment was lower than the treatment of keeping 70% of the field water holding capacity. The exchangeable calcium of the treatment of high quantity of raw phosphate rock was o.18 more than the treatment of low levels of the raw ground phosphate rock. Content of exchangeable calcium of flooded treatment was higher than the treatment of keeping 70% of the field water holding capacity. Adding ground phosphate rock and rotten rice straw to soil increased the cation exchange capacity by 0.22 to 1.44cmol/kg.3) The treatment added phosphate rock and rotten rice straw changed the lead speciation significantly, reduced the form of exchangeable state of lead and increased the form of iron manganese oxide combining state of lead and residue state of lead which had a low biological effectiveness. In pot experiment, compared with the control, the exchangeable state of lead in treatments adding activated phosphate rock and rotten rice straw reduced by 35 mg/kg, a drop of 28.7%.While in cultivation experiment, the exchangeable state lead reduced by 4.5 to 50.8 mg/kg, compared with the control. The exchangeable state of lead in treatments adding rotten rice straw decreased by 4.8 to 13.2mg/kg, compared with the treatments not adding rice straw. The exchangeable state of lead of flooded treatment was lower than the treatment of keeping 70% of the field water holding capacity. Most of the exchangeable state of lead translated into iron andmanganese oxide combining state and residue state. The treatment added rotten rice straw had more organic combination state of lead than the treatment not added rotten rice straw. The iron manganese oxide combining state of lead in flooded treatment was higher than the treatment of keeping 70% of the field water holding capacity. The carbonate combination state of lead in these treatments did not changed significantly.4) The application of raw phosphate rock and activated phosphate rock improved soil p H value, inactivated heavy metal, and reduced heavy metal content in the crops,and promoted crop production in field experiment. In paddy soil, the application of activated phosphate rock increased soil p H by 0.22 after harvesting the rapeseed, and increased by0.10 again after harvesting the rice. After harvesting the rapeseed, the application of activated phosphate rock decreased exchange state of lead and zinc to 25.3 mg/kg and45.2 mg/kg, with a decline of 35% and 39%. The application of activated phosphate rock reduced the concentration of lead and zinc by 43% and 24% in rapeseed, and increased the production by 234 kg/ha, with a growth rate of 16%, compared with the control. After harvesting the rice, the application of activated phosphate rock continued to reduce the exchange state of lead and zinc, and continued to decrease the concentration lead and zinc, reducing by 40% and 27%, in respectively. Compared with the control, the application of activated phosphate rock raised yield of rice by 604 kg/ha, with a growth rate of 7%.In summary, the paper showed that activated phosphate rock promoted the passivation lead, and was better than raw phosphate rocks, phosphate rock mixed with rotted straw significantly improved the residue state of lead, but with raw straw had no significant effect, the flooded treatment could significantly improve the passivation effect,compared with the treatment of keeping 70% of the field water holding capacity. The paper got an understanding of the effect of the different passivation materials under different conditions on the lead passivation, and the effect was analyzed and discussed. A theoretical basis for soil lead pollution governance was provided, but the mechanism of the interaction between different materials and effect under different conditions on lead need further study. |
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