Field In-Situ Remediation Of Cu-Cd Polluted Soil By Amendments

The effects of six amendments, lime, apatite, montmorillonite, attapulgite, charcoal and pig manure, on in-situ remediation of Cu-Cd contaminated soil nearby a copper smelter were studied. Ryegrass(Lolium perenne L.) was planted in the experiment to examine the effect of the amendments on behaviors of copper and cadmium in soil-ryegrass system. And then lime, apatite, montmorillonite and attapulgite in 3 concentration gradients were selected for the choose of the best amendment and additive proportion were choosed by experiment. The results showed were as follows:Part one. Field in-situ remediation of Cu-Cd polluted soil by differnt amendments1. The six amendments had the abilities to increase pH and promote the transformation of Cu and Cd from the active forms to the inactive ones. In order to increase the biomass and Cu and Cd bioaccumulation quantity of ryegrass, these amendments have the ability to decrease the toxicity of Cu and Cd. Ryegrass experimental analysis revealed that the metals uptake of plant were depended on the existing chemical states of Cu and Cd. Cu content in shoots of ryegrass was positively correlated with EX-Cu in soil. And Cd content in shoots and roots of ryegrass was positively correlated with WSA-Cd in soil.2. Biomass and Cu and Cd bioaccumulation quantity of ryegrass were cited as indexes for evaluation of remediation effect of the amendments. And the effects of amendments were in the descending order of lime, apatite, charcoal, pig manure, attapulgite and montmorillonite.Part two. Field in-situ remediation of Cu-Cd polluted soil by amendments with different dosage.1. The four amendments, i.e. lime, apatite, montmorillonite and attapulgite, had the abilities to increase the biomass, Cu and Cd bioaccumulation quantity of ryegrass. And the remediation effects of lime, apatite and montmorillonite were improved with increasing dosage. The best effect in enriching Cu-Cd was obtained in the ryegrass of S3 (0.4% of the polluted soil of the plow layer) and L3 (2.32% of the polluted soil of the plow layer). And the value of relative absorption of Cu and Cd in the S3 is increased by 82 times and 67 times, respectively, compared with Control (no amendment), while they increased 81 times and 74 times in the L3, respectively.2. Amendments of lime, apatite, montmorillonite and attapulgite can increase soil pH and decrease available Cu and Cd concentrations in the soil. The four amendments promoted the transformation of Cu and Cd from the active forms to the inactive ones. Lime and apatite had a better effect of decreasing the EX-Cu and EX-Cd concentrations in the soil. Compared with Contral, treatment S3 decreased EX-Cu, EX-Cd contents by 96.4%-98.6%,16.8%-31.9%, respectively,; While that were 92.0%-97.2%,18.3%-27.7%, respectively, with treatment L3. That is to say, the chemical inactivation of Cu by the amendments was more effective than that of Cd.3. The four amendments increased the activitis of urease, acid phosphatase and calatase in soil, and the effects were in the descending order of lime, apatite, attapulgite and montmorillonite. The increasing extent of the soil enzymic activities was improved with the increasing dosage of each amendment. All these three enzymic activities were negatively correlated with soil available Cu and Cd, EX-Cu and EX-Cd, but positively correlated with soil pH.4. The physiological indexes of ryegrass were influenced by lime and apatite to different degree. With the increase of dosage of lime and apatite, the MDA content of ryegrass decreased, while CAT and POD activities increased. There were significant differences (p<0.05) in MDA content, CAT and POD activities, but no significant difference in SOD activity among lime or apatite with different dosage. The physiological indexes of ryegrass were correlated closely with soil available Cu and Cd, EX-Cu and EX-Cd, and soil enzymic activities.5. The amendments increased soil solution pH, but decreased Cu and Cd concentrations in the soil solution. Soil solution pH was negatively correlated with Cu and Cd concentrations in soil solution (p<0.01). And Cu concentration was positively correlated to Cd concentration in soil solution (p<0.01).In sum, this study cited ryegrass biomass, plant absorbability, chemical extractability and concentrations in soil solution of Cu and Cd, soil enzymic activities and ryegrass' physiological indexes for evaluation of the remediation effect of the amendments, and the treatments of S3 and L3 showed the best results. The application of using ryegrass with lime or apatite in Cu-Cd polluted soil is effective and deserves to be popularized.