Amelioration Of Humic Acid In Weathered Coal On Pb Contamibated Soil

As the rapid development of modern economy and expansion of city size, harmful heavy metals go into the soil through various means, resulting in serious pollution of soil. Heavy metal in soil not only causes soil degradation, affecting crop yield and quality decline, but also pollutes surface water and groundwater through runoff and leaching, endangering human health. Lead, a toxic heavy metal, will be difficult to exclude once entered the body. Lead directly damage human brain cells, particularly fetal nervous system, it can cause congenital mental retardation; on the elderly can cause dementia. There are also carcinogenic, mutagenic and other effects. Therefore, to find reasonable and effective, be passive or to extract various kinds of heavy metal, without destroying soil structure and the low cost, efficient, environmentally friendly repair agents alleviate heavy metal pollution has become an important part of mechanism.Humic acid is a complex molecules natural organic, a product of decay plant residue decomposition.The molecule contains carbonyl, carboxyl, hydroxyl and phenolic hydroxyl and other active functional groups, be able to combine with heavy metals, thus affecting transformation, mobility and bioavailability of heavy metal in the soil environment. Existing research shows that:humic acid have a higher adsorption capacity to metal ions. Humic acid extracted from the weathered coal have similar structures and properties with natural humic acids from soil organic matter. Long-term uses of weathered coal humic acid have significant effects on soil physical and chemical properties. So, application of coal humic acid substances as a purification vector of environmental pollutant is feasible and realistic.The test was to study the effect of coal solid waste-weathered coal humic acid not only on remediation of lead contaminated soils but also on soil physical and chemical properties, and provides a theoretical basis for the treatment of soil heavy metal pollution. The major results were summarized as follows:1. Leaching column experiments were set-up to investigate the effects of weathered coal humic acid (weight percentage content is 0.00%,0.50ï¼…,1.00%,2.00%)and simulated acid rain (pH=5.5,4.5) on leaching properties of lead. The results showed that:in the year of rainfall (438 mm), the application of weathered coal humic acid can reduce the lead concentration of soil leachates, especially in the levels of high concentration of 1000 mg/kg lead pollution, reduce the effect more pronounced. At the same time, the application of weathered coal humic acid can improve the soil leachate pH value, and the higher humic acid content, the higher pH value of soil leachates, effect of simulated acid rain of pH=4.5 and 5.5 on pH value of soil leachates is not significant.Application of weathered coal humic acid can effectively reduce soil pH value, leaching with diffent pH value of simulated acid rain, soil pH value of every layer showed a decreasing trend with the increase of humic acid content in soil, and soil pH value is not significantly different between different pH values of simulated acid rain.Application of 0.05% humic acid in 250mg/kg lead contaminated soil, surface soil available lead content was lower significantly 31.7%, pH=4.5 simulated acid rain leaching. Pb available content of every layer else treating soil have no significant changes, and effect of simulated acid rain of pH=4.5 and 5.5 on available lead content of every layer is not significant.2. Effect of different content humic acid on soil physical and chemical properties, rape growth and heavy metal characteristics at the different levels of lead pollution by a pot experiment. The results indicated:weathered coal humic acid can inhibit the transfer of lead to plants, and reduce the accumulation of lead in the rape. Humic acid can effectively reduce the migration, transformation and toxicity of lead in soil, because the humic acid has strong adsorption and chelation with lead ions. Weathered coal humic acid suppress the soil lead bioavailability by regulating the pH value and organic matter content of soil, and soil pH value is the dominant factor. Weathered coal humic acid can improve the soil structure, while increasing soil organic matter content, provide nutrients source for soil.It can be seen that to exert a certain amount of weathered coal humic on soil acid can increase soil fertility and effectively reduce the hazards of toxic heavy metals.