Preparation And Characterization Of Modified Clays And Its Passivating Effect On Availability Of Chromium In Soils

The industrial activities during the development of social economic have resultedin widely spread contamination of heavy metals in environment, especially from theindustries related with the metal processing. For the planting of landscape plants, thecontaminated soils by heavy metals also posed obviously negative effects on theirgrowth. Methods in this study, through the combination of chemical stability andPhytoremediation of contaminated soil remediation of chromium. Firstly,12kinds ofplant seeds germination test of chromium stress are done, screening2strong toleranceof plant Brassica juncea and Helianthus annus, and then the pot experiment. I preparedmodified clays with iron or sulfhydryl chemicals, or both of iron and sulfhydrylchemicals to passivate and decrease the availabilities in growth of landscape plants. It isaimed that the results of this study can provide new environmental materials forsafeguarding the growth of plants on chromium contaminated soils.In the study, three kinds of modified clays were prepared with hydrothermalmethod. One was modified clay only with zero valent iron （ZⅥ） named as Fe-MO, andthe other two were modified clays with both of ZⅥ and sulfhydryl chemicals withdifferent modified procedures named as CM1and CM2, respectively. The adsorptionexperimental results for Cr（Ⅵ） removal in aqueous solution show that the modified clayof CM1had the highest adsorption capacity for Cr（Ⅵ）, while the modified clay of CM2has the highest adsorption rates for chromium removal. The different reactionconditions exerted important effects on chromium removal with these two iron-sulfhydryl modified clays. The observed optimal conditions for chromium removal withCM2were at acidic condition when with the initial CM1dosage of1.5g·L^-1and initialCr（Ⅵ） concentration of1-2mM. Our study results also show that the obtained modifiedclays jointly with iron and sulfhydryl not only decontaminate chromium with adsorptionprocess, and Cr（Ⅵ） with higher toxicity can also be partly reduced to Cr（Ⅲ） with lowertoxicity due to the reducibility of iron modified in the clays. The passivating effect of chromium availabilities during growth of plants incontaminated soils were also investigated with potting experiments, in which Brassicajuncea, Helianthus annus and Tagetes patula were used as the target plants. The resultsshow that the growths of both of the two plants were obviously inhibited when plantedin chromium contaminated soils.However, when the chromium contaminated soils were modified with a certainratio of obtained iron-sulfhydryl jointly modified clays, the plants grown without anyinhibition experience. By measuring the growth index of plant height, stem diameter,leaf area, wet weight and dry weight, and the Chromium contents in soil and plant,which indicated that when with modified clay in the chromium contaminated soils, theavailabilities of soil chromium for plant growth were largely inhibited, and the plants insoils modified with the obtained clay materials can grow normally.