Research On The Passivation Mechanisms Of Soil Heavy Metals (Cd, Pb) With Different Sizes And Levels Of Phosphate Powder

The adsorption and desorption of Cd, Pb in the aqueous solution of phosphate powder, Effects and mechanisms of different sizes and levels of phosphate powder on the availability of Cd and Pb, heavy metals reducing mechanisms of phosphate powder on contents of plant Cd and Pb in different growth periods of rice were studied in the paper. The main results are as follows:1. When pH and concentration of Cd, Pb were certain, different oscillation time. The adsorption and desorption of Cd, Pb with different sizes of phosphate powder (0.1μm>0.5μm、1.5μm、15μm、30μm、150μm、300μm) were increasing with the increase of oscillation time, finally, reaching balance. The finer the size of phosphate powder, the higher the adsorption rate, but the lower the desorption rate. Among seven sizes, there were little differences in smaller sizes (0.1μm、0.5μm、1.5μm), having shorter balance time. But in bigger sizes (30μm、150μm、300μm), the differences were striking, taking longer balance time. When the pH value was different with certain oscillation time and concentration of Cd, Pb, the adsorption rates of Cd and Pb in phosphate powder with sizes of0.1μm,1.5μm,30μm,300μm were increasing with the increase of pH value, but the desorption rates were decreasing. When the pH was6, the adsorption and desorption rates reach equilibrium in those four sizes, and the smaller size, the smaller effect of pH on the adsorption desorption.2. The yield, leaf area and total phosphorus content of rape were increased with the level of phosphate powder in the same size. While contents of Cd and Pb in plant and the available form of them in soil were decreased, with the increase of percent of the residual form. The same was found in phosphate powder with the same dosage and different size. The correlation of Cd and Pb between plant aboveground and available form in soil was some positive. Effect of phosphate powder on soil pH value was related to the level, not the size of them, as soil available phosphorus was related to the level and size.3. The growth and yield of rice in different growth periods had no significant difference, when the size of phosphate powder was0.1μm. The same result was found during tillering stage with300um size of phosphate powder. With0.1μm phosphate powder, the Cd content was significantly reduced in the flowering period, as was the Pb content in transplanting phase, which was decreased mostly by the morphological analysis of Pb in soil. Effects of phosphate powder on soil pH value and available phosphorus were related to size, level, irrelevant to adding period.