Shuzo Tokunaga

Evaluation of remediation process with plant-derived biosurfactant for recovery of heavy metals from contaminated soils

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.

Acid washing and stabilization of an artificial arsenic-contaminated soil.

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.

Extraction of heavy metals from MSW incinerator fly ashes by chelating agents.

An extraction process has been studied on a laboratory scale for the pretreatment of municipal solid waste (MSW) incinerator fly ash to remobilize Cr, Cu, Pb, and Zn. Five different types of fly ashes were treated with HCl, nitrilotriacetic acid (NTA), ethylendiaminetetraacetate (EDTA), or diethylenetriaminepentaacetate (DTPA) in a batch process in the pH range 2.5-10. The extraction of heavy metals by HCl was dependent on pH, increasing with increasing acid concentration. The efficiency of the chelating agents was independent of pH. By the treatment with 3.0% EDTA or DTPA, 20-50% of Cr, 60-95% of Cu, 60-100% of Pb, and 50-100% of Zn were extracted in the pH range 3-9. NTA was also effective in extracting Cr, Cu, and Zn. The maximum extraction of Cr, Cu, Pb, and Zn was obtained at 0.3-1.0% concentration of the chelating agents. NTA was effective in extracting Pb at a concentration as low as 0.1%. Extraction behavior of other elements during the treatment was also studied. The leaching test on the residues after the treatment with chelating agents showed that the fly ashes were successfully detoxified to meet the guideline for landfilling.

Removal of hazardous anions from aqueous solutions by La(III)- and Y(III)-impregnated alumina

New adsorbents, La(III)- and Y(III)-impregnated alumina, were prepared for the removal of hazardous anions from aqueous solutions. A commercially available alumina was impregnated with La(III) or Y(III) ions by the adsorption process. The change in the surface charge due to the impregnation was measured by acid/base titration. The adsorption rate and the capacity of the alumina for La(III) and Y(III) ions were determined. The adsorption characteristics of the La(III)- and Y(III)-impregnated alumina and the original alumina for fluoride, phosphate, arsenate and selenite ions were analyzed under various conditions. The pH effect, dose effect, and kinetics were studied. The removal selectivity by the impregnated alumina was in the order fluoride > phosphate > arsenate > selenite. The impregnated alumina has been successfully applied for the removal of hazardous anions from synthetic and high-tech industrial wastewaters.

Extraction of heavy metals from MSW incinerator fly ash using saponins

An extraction process with saponins was evaluated for removing heavy metals from MSW (municipal solid waste) incinerator fly ashes. Two different fly ashes, A and B, were treated on a laboratory scale with three triterpene-glycoside type of saponins, M, Q, and T, in the pH range 4-9. The results were compared with those of the HCI and EDTA treatment. The treatment with saponins extracted 20-45% of Cr from the fly ashes. Saponins were also effective in extracting Cu from fly ash A attaining 50-60% extraction. Saponin T extracted 100% of Pb from fly ash A at pH around 4. The extraction of Zn with the saponin treatment was similar to that of the HCl treatment. Further, Cr, Cu, Pb, and Zn were fractionated by sequential extraction to investigate the effect of saponins on each fraction. Extraction behavior of other elements during the saponin treatment was also studied. The leaching test on the residues received after the saponin treatment showed that the fly ashes were successfully detoxified to meet the landfilling guideline.

Chemical Extraction of Arsenic from Contaminated Soil

A series of batch extraction experiments were conducted using a fortified soil with different extracting solutions such as inorganic acids (hydrochloric acid (HCl), sulfuric acid (H2SO4), phosphoric acid (H3PO4), perchloric acid (HClO4), or nitric acid (HNO3)), organic acids (acetic acid (C2H4O2), citric acid (C6H8O7)) and alkaline agent (NaOH). Various concentrations were used to investigate the removal efficiency and to optimise the concentration of each extractant. In the present investigation a Kuroboku soil contaminated with arsenite (As(III)) was used as a model soil. Arsenic was extracted most efficiently by 5% H3PO4 with a maximum of more than 99% from the model soil. Sulfuric acid also showed high percentage extraction efficiency. On the other hand, C2H4O2 and oxidizing acids such as HNO3 and HClO4 showed low efficiency of As extraction compared with C6H8O7. Although, NaOH also showed higher extraction efficiencies compared with organic and oxidizing acids but mainly arsenate (As(V)) was found to be the major component. A significant fraction of the As(III) was oxidized to As(V) during mineral acid and alkaline extraction and extraction efficiency also varied with the concentration of the acid and alkali solution.

Using aspergillus niger to bioremediate soils contaminated by heavy metals

Abstract A bioremediation process was developed using the fungus AspergiUus niger to produce weak organic acids for the leaching of heavy metals from contaminated soils. The fungus was cultivated on the surface of three contaminated soils (a clay loam, a loam, and a sandy clay loam) for 15 days at 30°C and at a pH <4 to favor the production of citric acid rather than oxalic acid which hinders Pb leaching. For the clay loam, Cr, Mn, Pb, and Hg were leached to levels of 37, 41, 85, and 91%, respectively. For the loam, the leaching of Cd and Pb was found to reach levels of 99.7 and 83%, respectively. For the sandy clay loam, Cd, Cu, Pb, and Zn were leached to levels of 99,94,58, and 99%, respectively. The three contaminated soils could have been remediated to the A category of the Province of Quebec standards for heavy metals after 20 to 25 days of leaching using this technique.

Extraction of heavy metals from a contaminated soil using citrate-enhancing extraction by pH control and ultrasound application.

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 4 h, 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 24 h, showing the enhancement of heavy-metal removal. Thus, the performance of citrate for removing heavy metals was improved.

Removal of arsenic from contaminated soils using different salt extractants.

This study presents an environmental-friendly and cost effective method for the extraction of arsenic from contaminated soils. Laboratory experiments using inorganic salts, potassium phosphate (KH2PO4), potassium chloride (KCl), potassium nitrate (KNO3), potassium sulfate (K2SO4), and sodium perchlorate (NaClO4) were evaluated as arsenic extractants. An Andosol soil was artificially contaminated with arsenite [As(III)] and arsenate [As(V)]. The soil was washed in a batch process with different salt solutions in the pH range 3–11 for 24 hours at 20°C. Among the various potassium and sodium salts tested, KH2PO4 was found to be highly effective in extracting arsenic from As(III)-soil attaining more than 80% and 40% from As(V)-soil in neutral pH range. Other salts were particularly ineffective in extraction of arsenic from both soils. More arsenic was extracted more from the As(III)-soil than the As(V)-soil.