Research On Selection Of Amendments And The Immobilization Effects Of Arsenic And Cadmium Contaminated Farmlands

In recent years, the heavy metal pollution of soil has increasingly become one of the important environmental problems with the widely contaminated area and serious hazard. As an effective remediation technology in the field of As contaminated soils remediation, the chemical immobilization technology has received more attention due to its simple, economic, and efficiency. However, seeking for efficient passivation materials and producing well performance passivants are the focus and bottle neck of the technology. Most of the heavy metal pollutions of soil in China are combined pollutions, especially for arsenic and cadmium combined contamination. Therefore, nowadays the prominent problem in heavy metal contaminated area is lack of correct remediation technology, and safe use of farmlands with excessive arsenic and cadmium is an urgent task. In this study, a variety of functional materials with good adsorption of arsenic and cadmium were screened and prepared based on the stabilization effect of arsenic and cadmium in farmland. Soil cultivation and pot experiments were designed to explore passivation effects of the materials on the arsenic and cadmium in soil and identify the corresponding passivation influence on the availability of arsenic and cadmium in soils, then establish the safe utilization model tentatively, which could provide scientific basis for safety production in the farmlandswith excessive arsenic and cadmium.Main results are as follows:1. By comparing the adsorption capacities of different materials for As(V) and Cd in solution, we found that zero-valent iron, iron modified biochar, acid-modified red mud, iron modified carbon had stronger adsorption capacities than other materials such as red mud, bentonite, natural zeolitefor arsenic with a removal rate of 70% As(V). However, in the case of Cd, the removal rates of Cd of the materials such as zero-valent iron, biochar and modifiedbiocharwere also over 70%, except for those of concentrated acid-modified red mud and bentonite. Overall, iron modified biochar and zero-valent iron had better adsorption capacity for Cd and As(V).2. The result of thermerical adsorption indicated that the progress of adsorption was perfectly fit to the adsorption kinetics quasi-two equation, and its determination coefficient is ranged from 0.98 to 1.00. The calculated theoretical equilibrium adsorption is in good agreement with the maximum equilibrium adsorption which is obtained from test. The adsorption isotherm of different agricultural waste straw biochar and its iron modified materials to As(V) and Cd met isotherm equation, and the correlation coefficient was above 0.71, which indicated that these materials can adsorb As(V) and Cd mainly through physical method not through chemical method.3. Different iron modified biochar materials(IMB)(straws originated from maize, rice and weed) were spiked into the soil with different ratio(w/w)of 1%, 2% and 4% for soil cultivation experiment. The result revealed that all the treatments of iron modified biochar can significantly reduce the content of Olsen-As, EDTA-Cd in soil and 4% IMB achieved best effect of all the amendments with the amended rate of As and Cd 13.5% and 42.9% respectively.This amended effect is related to the transformation of available As and Cd to residual As and Cd.4. Pot experiment indicated that the addition of different mixture of arsenic modified biochar and zerovalent iron in different ratio into soil presented a significant effect on pakchoi cabbage. Compared with CK, the biomass of pakchoi cabbage increased significantly with the amount of iron modified biochar while 1% treatment decreased the biomass of pakchoi. Under the co-work of iron modified biochar and zerovalent iron, the growth of plant were improved evidently. Especially co-work of 1% iron modified biochar with 0.1% and 0.5% zerovalent iron, with the biomass increased 63.4% and 71.8%, which are much better than addition of zerovalent iron alone.5. The situations of uptake Cd by pakchoi cabbage were different after the addition of different ratio of biochar, iron modified biochar and zero valent iron into soil. The addition of iron modified biochar decreased the uptake of Cd and As by pakchoi obviously. The reduced percentage of As uptake by rape reached 33.3% and 42.9% respectively for 1% and 4% IMB treatment, and those of Cd uptake in corresponding treatments for were 27.4% and 45.2%, seperately. Under the treatment of original biochar, though it performed good effect on Cd amendment, it increased the uptake of As by plants. Under the treatment of iron modified biochar and zerovalent iron, 4% iron modified iron biochar combined with 0.5% zero-valent iron, and 1% iron modified iron biochar combined with 0.1% zero-valent iron, and 1% iron modified iron biochar combined with 1% zero-valent iron, all presented good effect on remediation of As and Cd contaminated farmland. What’s more, the combination of 1% iron modified iron biochar combined with 1% zero-valent iron can decrease the uptake of Cd in 42.9% and 74.0% and improve the quality of crop greatly.