Remediation Of Cu-Contaminated Soils With Several Materials

Heavy-metal pollution is a primary type of soil contamination. The heavy metals can enter into groundwater and food chain, or be absorbed by the plants directly, and lead a serious threat to ecological environment and people's health. Therefore, why to treat the soil heavy metal pollution becomes the focus of various scientific workers. Also, it is the hot topic of the community and the keypoint of environmental pollution control. Due to its obvious effect and simple operation, the chemical remediation technology has been widely used.Cu is one of the essential micronutrients of plants growth, and a kind of heavy metal elements of environmental pollution. The objective of this study is to explore Cu-contaminated-soil remediation with mineral materials. The variable charge soil-red soil and constant charge soil-yellow brown soil were selected, and were polluted with exogenous copper. The man-polluted soils and natural polluted soil were remediated with phosphate rock, blast furnace slag particles, blast furnace slag, Na-bentonite, diatomite and their modified products. The different forms of Cu were analyzed with the modified BCR extracting technology. The effects of materials type and dosage, temperature and soil type, pH, medium concentration and flooded condition on the form transformation of Cu in soil were discussed. The results show that:1. Phosphate rock, bentonite, diatomite had a certain passivation effects on Cu in soil. After modified by oxalic acid, the Cu adsorption ability of phosphate rock was poor than the original ore. When 8% dosage of phosphate rock was added into the polluted soils, content of soluble Cu decreased to 25.96%, residual Cu increased to 82.55%. However, comparing with the CK, the content of soluble Cu in soil did not vary, and the residual Cu increased to 77.07% with modified phosphate rock. The passivation effect of modified bentonite and diatomite on Cu in soil significantly increased. With 10% dosage of these materials, the soluble Cu decreased to 79.08% and 47.52%, residual Cu increased to 78.06% and 72.85%, respectively. The passivation ability of blast furnace slag was more than that of iron on Cu. When 10% dosage of steel slag applied, soluble state decreased to 21.22%, residual ones increased to 29.67%.2. Comprehensively comparing with the modified phosphate rock (A2), blast furnace slag particles (B2), modified bentonite (C2) and modified diatomite (D2), it was 3 best one. Application of 5% dosage of modified bentonite in soils, the soluble Cu reduced to 84.47%,92.36%,91.02%, reduced state to 93.24%,76.58%,91.57%, oxidation state to 121.06%,299.19%,246.70%, and residual stat to 146.20%,140.72%,93.46%, respectively. The content of soluble and reduced state copper greatly reduced, and the oxidation and residual state increased highly.3. When the exogenous copper was added into soil, after 30d, the Cu formation distribution of constant charge soil was close to that of natural soil, but in man-made Cu soil, the content of soluble Cu was higher. The Cu passivation ability of four materials increased as cultivating prolonged. Applied 5% modified bentonite, content of soluble modal was gradually decreasd to 0.34% and 16.16%, to 9.83% and 38.96% with residual state,respectively. It illustrated that Cu adsorption was a balanced process by materials. As the temperature increased from room temperature to 35℃, content of soluble Cu also declined, residual state rised gradually. With 0.1% dosage used, soluble state Cu decreased by 24.16% and 3.02%; when 5% dosage, residual Cu content was 45.95%,48.20%,49.86%, increased by 11.15% and 3.44%.4. With the increase of modified bentonite dosage, the pH three kinds soil increased gradually, and in acidic soils, water added also could improve the soil pH. As pH increased, heavy metal adsorption ability of three soils strengthened gradually. The content of soluble Cu gradually reduced, residual Cu increased gradually, as followed R3>R1>R2. When the pH of soils reached 6, soluble Cu droped to 9.93%,17.69%, 41.97%, residual Cu fell to 11.49%,13.33%,15.76%, respectively. But the variation of constant charge soilI was more than that of the variable charge soil, It could mean that under the same conditions, Cu adsorption ability of constant charge soil was stronger than that of variable charge soil. After flooded, in reductive condition, oxidation state Cu increased relatively to the normal conditions and the other three forms lessened, but all the amplitude change was small.5. When the medium concentrations of NaCl increased, content of soluble Cu increased gradually, and content of residual Cu gradually reduced, and the order is as follows:R1>R3>R2. When the NaCl concentration was 0.1mol·L-1, content of soluble Cu in three soils increased to the maximum,6.31%,24.31%,34.55%, respectively. The content of residual Cu reduced to the maximum 3.72%,3.47%, and 4.84%, respectively. It is clear that with ionic strength increase, Na+ could compete with Cu2+, the capabilities of Cu adsorption in constant and variable charge soil lowered, but the decline in constant charge soil was more than that of variable charge soil. And it was found that with pH and concentration of the NaCl increased, all the man-made polluted soil's variation amplitude were bigger. It could explain that the ageing process of exogenous copper in the soil was a long stage, and different forms Cu were unstable in the man-made polluted soil, easy to change with external conditions.To sum up, the materials modified are more powerful than the original materials on Cu in soil. The effect of modified bentonite with DTC on Cu passivation is the best one of the selected four kinds of materials. After 60d, at room temperature, when 5% dosage was added, content of soluble Cu is from2.52% to 4.13%, reduction state Cu is from 2.90% to 3.49%,2.90%, oxidation state Cu is from 44.26% to 51.45%, residual Cu content is from 43.09% to 48.12%. It stated that Cu can largely been fixed in soil. With extension of time, rise of temperature and pH, the content of Cu fixed in soil will increase, but with the increases of electrolyte concentration, the effect is just the opposite.