Soil Washing Of Lanthanum Contaminted Soil By Using Tartaric Acid, Citric Acid And Malic Acid

To investigate the influence of chemical concentration, time, and pH on soil leaching, three organic acids were analyzed for leaching efficiency of oscillated lanthanum-contaminated soils. The study was performed under varying concentrations (0.05%,0.1%,0.2%,0.5%,1%), time (0.5 h,1 h,2 h,4 h,8 h), and pH (3,5,7,9,11) and the effect on soil organic matter, total nitrogen, total phosphorus and total potassium levels were monitored. The main results are as follows:The leaching rate of lanthanum contaminated soil (300 mg kg-1) by tartaric acid, malic acid, and citric acid increased by concentration linearly and equally curve power function (P< 0.05) at a specific time length (0.5 h,1 h,2 h,4 h,8 h), where the highest rate is between 27.1% to 46.29%. Under the same leaching chemical concentration, the leaching rates of these three acids increase with leaching time at linear exponential function. Overall, malic acid leaching rate is the highest, while tartaric acid leaching rate is the lowest. The optimal concentration of tartaric acid is 1% while both citric acid and malic acid have the optimal concentration of 0.5%. The optimum leaching time for these three kinds of low molecular weight organic acid is 4 h.Additionally, the leaching rate of lanthanum contaminated soil (2500 mg kg-1) by tartaric acid, malic acid and citric acid also increase by concentration linearly and equally curve power function (P<0.05) at a specific time length (0.5 h,1 h,2 h,4 h, 8 h), in which the highest rate is between 45.89% to 59.84%. Under the same leaching chemical concentration, the leaching rate increased with leaching time by linear quadratic function. Overall, the leaching rate of citric acid is highest while that of the tartaric acid is the lowest leaching. The optimal concentration of tartaric acid is 1%, while both citric acid and malic acid has the optimal concentration of 0.5%. The optimum leaching time for all three acid is 8 h.The leaching results on soil lanthanum by leaching chemical varied with pH levels. Leaching rate of tartaric acid on soil lanthanum decreased first, then increased and finally decreased (P<0.05) with increasing pH. The leaching effects are the worst at pH 11and optimum at pH 3 (P<0.05). However, citric acid with increase pH initially had increasing leaching rate on the soil lanthanum and subsequently decreased with optimum leaching effect at pH=5 and worst at pH 3(P<0.05). The leaching rate trend of malic acid with the increase of pH is similar to that of citric acid: initial increase and subsequent decrease with optimum leaching effect at pH 5 and worst at pH 11(P<0.05).This study has shown that different leaching chemicals have different effects on the soil properties. For example, the loss of soil organic matter caused by tartaric acid is less than that of citric acid and malic acid while loss of soil organic matter remains constant with the increase of pH (P<0.05). Soil total nitrogen loss caused by malic acid and citric acid is less than tartaric acid, but with the increase of leaching chemical pH, their effect on total nitrogen loss gradually decreases (P<0.05). Total phosphorus loss of soil follows similar trends with total nitrogen loss (P<0.05); the loss caused by citric acid is greater than tartaric acid and malic acid. Soil total potassium levels remain undisturbed by the leaching chemicals (P<0.05) unlike total nitrogen and phosphorus levels.