ABSTRACT
A novel extraction method has been developed for remediation of a heavy-metal contaminated soil. Citrate was used as environmentally-friendly extractant to remove Pb, Zn, Cd, and Cu. Heavy metals were extracted effectively at two different pH regions around 2 and 4-5. Kinetic study showed that heavy metal extraction by washing at pH around 2 reached equilibrium within 4h, while extraction by washing at pH 4-5 increased gradually by the end of 24 h washing. Washing extraction at pH 2 for 6 h which was followed by washing at pH 5 for 16 h increased the percentage extraction of Pb and Cu from 67.6 to 85.9% and from 77.5 to 83.4%, respectively. Ultrasound application has been also investigated to enhance extraction of heavy metals by using citrate. Only 30 min ultrasound application at 19.5 KHz attained higher extraction of heavy metals than those by washing for 24h, showing the enhancement of heavy-metal removal. Thus, the performance of citrate for removing heavy metals was improved.
Subject(s)
Chelating Agents/chemistry , Metals, Heavy/chemistry , Soil Pollutants/analysis , Water Purification/methods , Decontamination/methods , Humans , Hydrogen-Ion Concentration , UltrasonographyABSTRACT
A washing process was studied to evaluate the efficiency of saponin on remediating heavy metal contaminated soils. Three different types of soils (Andosol: soil A, Cambisol: soil B, Regosol: soil C) were washed with saponin in batch experiments. Utilization of saponin was effective for removal of heavy metals from soils, attaining 90-100% of Cd and 85-98% of Zn extractions. The fractionations of heavy metals removed by saponin were identified using the sequential extraction. Saponin was effective in removing the exchangeable and carbonated fractions of heavy metals from soils. In recovery procedures, the pH of soil leachates was increased to about 10.7, leading to separate heavy metals as hydroxide precipitates and saponin solute. In addition recycle of used saponin is considered to be effective for the subsequent utilization. The limits of Japanese leaching test were met for all of the soil residues after saponin treatment. As a whole, this study shows that saponin can be used as a cleaning agent for remediation of heavy metal contaminated soils.
Subject(s)
Decontamination/methods , Metals, Heavy/isolation & purification , Saponins/chemistry , Soil Pollutants/isolation & purification , Surface-Active Agents/chemistry , Biotechnology/methods , Chemical Fractionation , Conservation of Natural Resources , Kinetics , Plants/chemistryABSTRACT
An acid-washing process was studied on a laboratory scale to extract the bulk of arsenic(V) from a highly contaminated Kuroboku soil (Andosol) so as to minimize the risk of arsenic to human health and the environment. The sorption and desorption behavior of arsenic in the soil suggested the possibility of arsenic leaching under acidic conditions. Artificially contaminated Kuroboku soil (2830 mg As/kg soil) was washed with different concentrations of hydrogen fluoride, phosphoric acid, sulfuric acid, hydrogen chloride, nitric acid, perchloric acid, hydrogen bromide, acetic acid, hydrogen peroxide, 3:1 hydrogen chloride-nitric acid, or 2:1 nitric acid-perchloric acid. Phosphoric acid proved to be most promising as an extractant, attaining 99.9% arsenic extraction at 9.4% acid concentration in 6 h. Sulfuric acid also attained high percentage extraction. The arsenic extraction by these acids reached equilibrium within 2 h. Elovich-type equation best described most of the kinetic data for dissolution of soil components as well as for extraction of arsenic. Dissolution of the soil components could be minimized by ceasing acid washing in 2 h. The acid-washed soil was further stabilized by the addition of lanthanum, cerium, and iron(III) salts or their oxides or hydroxides which form insoluble complex with arsenic. Both salts and oxides of lanthanum and cerium were effective in immobilizing arsenic in the soil attaining less than 0.01 mg/l As in the leaching test.
