Study On Immobilization Of Copper In Contaminated Soils By Organic-inorganic Complex

In recent decades, the contamination of soils by toxic and/or hazardous heavy metals is a widespread environmental problem and the removal of heavy metals from contaminated soils is becoming a major concern. Although several methods of remediation contaminated soils by heavy metals for a variety of pollution types and grades have been developed by a number of works, each method has its own application limitation. The immobilization is an economic, efficient and feasible remediation technique of contaminated soils by heavy metals, and it is suitable for the remediation of slight non-point pollution soils induced by agricultural activity, especially for the combined pollution of heavy metals. The heavy metals immobilization capability of organic-inorganic complex, such as adsorption, precipitation, condensation and complexation, is better than organic or inorganic materials individually. Undoubtedly, selection and application of organic-inorganic complex made of natural materials will reduce the remediation cost and environmental risk, and improve the remediation efficiency.In this study, a new organic-inorganic complex was synthesized using bentonite, zeolite (inorganic component) and pig manure, corn straw (organic component) for the immobilization of heavy metals in soil, and laboratory soil incubation experiments were conducted to investigate the sorption and desorption characteristics of Cu (Ⅱ) on organic-inorganic complex and examine the effect of organic-inorganic complex on the concentrations of DTPA-Cu (Ⅱ) (DTPA-extractable) in acid brown soil, aquic brown soil, and cinnamon soil respectively. The major objective of the present study is to provide some theoretical proofs of the development of practical and cost-effective remediation technology of heavy metals contaminated soils.The main results of this paper are as follows:1. The bentonite, zeolite, pig manure, and corn straw were selected, and the maximum adsorption capacity on copper (Cu (Ⅱ) ) was 4.119mg/g for Na-bentonite, 3.769mg/g for Ca-bentonite, 3.812mg/g for zeolite, 2.652mg/g for pig manure and 2.341mg/g for corn straw. The carbon-nitrogen ratio (C/N) of pig manure was more beneficial to microbial growth and propagation than it of corn straw, so the degradation rate of the former was faster than the latter. Therefore, Na-bentonite and pig manure were optimum raw materials for the preparation of organic-inorganic complex.2. The 4 technical coefficients for the preparation of organic-inorganic complex with the Na-bentonite and pig manure were investigated. The results indicated that the optimum process conditions was the 10% degradation solution of pig manure with Na-bentonite and the weight ratio was one third (W pig manure: W Na-bentonite = 1:3), pH value was 6~8, the reaction temperature was 60℃, and mixing reaction time was 2.5 hours. Both the surface of complex prepared by optimum process conditions and the surface of Na-bentonite were with negative charges, but the Zeta potential of former was higher (-38.7mv) than it of latter (-48.0mv). There was slight different in morphology between the two, and the particle of Na-bentonite was tightened, and organic-inorganic complex was looser.3. The adsorption curve of Cu (Ⅱ) on the surface of the organic-inorganic complex could be described well with Langmuir and Freundlich isotherm models. The average desorption rate of easy desorption Cu (Ⅱ) released by 0.1mol/L KNO3 was lower than hard desorption Cu (Ⅱ) released by 0.1mol/L HCl, and the Cu (Ⅱ) asorbed on the organic-inorganic complex might be hard desorption Cu (Ⅱ). The results indicated that the organic-inorganic complex was feasible for the heavy metals immobilization in contaminated soils because of its strong adsorption capacity.4. There were the difference of parent materials among acid brown soil, aquic brown soil, and cinnamon soil, so the effect of organic-inorganic complex on the concentrations of DTPA-Cu (Ⅱ) in three soils was significantly different. The organic-inorganic complex could significantly reduce the concentrations of DTPA-Cu (Ⅱ) in aquic brown soil, and there was no significant difference between the direct applying the organic-inorganic complex to soil and it bagged. However, no certain rules of the effect of organic-inorganic complex on the concentrations of DTPA-Cu (Ⅱ) could be found in acid brown soil and cinnamon soil. The parent material of soil might be one of the major effect factors of the organic-inorganic complex applying to the remediation of heavy metals contaminated soils.5. The direct applying the organic-inorganic complex to soil and it bagged significantly decreased the pH value in acid brown soil and increased in aquic brown soil, but no significant regularity could be found in cinnamon soil. The soil pH value was significant linear correlated with the concentrations of DTPA-Cu (Ⅱ) in soils. So it could be assumed that increasing of the pH value in aquic brown soil after adding organic-inorganic complex induced the decreasing of the concentration of DTPA-Cu (Ⅱ). It might be one of main remediation mechanisms of heavy metals contaminated soils by organic-inorganic complex.In summary, it could be concluded from this paper that organic-inorganic complex prepared by Na-bentonite and pig manure degradation solution had proper immobilization capability of Cu (Ⅱ) in aquic brown soil, and it did not perform efficiently in cinnamon soil and acid brown soil which contained more montmorillonite, vermiculite in their clay minerals. The parent material of soil might be one of the major effect factors of the organic-inorganic complex applying to the remediation of heavy metals contaminated soils. The present study might provide some theoretical proofs of the development of practical and cost-effective remediation technology of heavy metals contaminated soils. More extensive research would be needed to further test this under field conditions.