Remediation Of Heavy Metal

Remediation of Heavy Metal Contaminated Soil

:Presented by Jamal suliman elgosni Under supervision of Dr Maher George Nassem

Introduction

(Heavy

metal (HM contamination of soils has

become a serious problem in areas of intense industry and agri- culture. HMs are deposited in soils by atmospheric input and the use of mineral fertilizers or compost, and sewage sludge disposal. Soils polluted with HMs pose a health hazard to humans as well as plants and animals, often requiring soil remediation practices. Conventional remediation methods usually involve excavation and removal of contaminated soil layer, physical stabiliza-tion (mixing of soil with cement, lime, apatite etc.), or washing of contaminated soils with strong acids or HM chelators (Berti et al., 1998, Steele and Pichtel, 1998)

Sources of Soil Contamination soils in both industrial parks and near small factories outside the parks are affected by a wide variety of contaminants. The most serious sources of soil contamination are (EPA/ROC 1994):

1. Heavy metals in hazardous waste, including materials from chemical production, dyeing, electroplating and heat treatment, the production of batteries, metal treatment, mining and extractive industries, scrap yards, service stations and 2. Hazardous organic waste materials, tanning including those from medical centers, oil production and storage, and paint and pesticide production 3. Corrosive metal waste materials, including those from acid/alkali plants and

Sources of heavy metals in soils and their expected ionic species in soil .solution

METALS AT CONTAMINATED SITES • Approximately 75% of Superfund sites for which Records of Decision (RODs) have been signed contain metals as a form of contamination. Some of these sites contain mixed metal-organic wastes for which metals might not be the primary contaminant of concern.

• The most common metals found at contaminated sites are (U.S. EPA, 1996b), in order: lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), and mercury (Hg). Figure 1 summarizes the frequency with which these metals occur at Superfund sites.

Figure 1. Metals Most Commonly Present in all Matrices at Superfund Sites (from U.S. (EPA, 1996

The range of contaminant concentrations and the physical and chemical forms of contaminants will depend on activities and disposal patterns for

The contamination level of trace elements in rural soils of the world

Remediation can be achieved in several ways: physical, chemical and biological

• Physical methods of remediation include verification, encapsulation, soil washing, artificial ground freezing, and electro kinetics

• The chemical methods use chemical treatment to remove or decrease the availability of metals to living things and groundwater, and they include neutralization, solidification • Biological methods make use of plants and microorganisms to remedy metal contaminated soil

Soil amendments for remediation

helating compounds • Recent research has shown that chemical amendments, such as synthetic organic chelates, can enhance phytoextraction by increasing HMs bioavailability in soil thus enhancing plant uptake, and translocation of HMs from the roots to the green parts of tested plants (Epstein et al., 1999; Huang et al., 1997). Of the chelates tested, ethylene diamine tetraacetic acid (EDTA) was often found to be the most effective (Blaylock et al., 1997).

• The addition of EDTA enhanced accumulation of HMs in green parts of the test plant. However, EDTA addition also caused leaching of Pb, Zn and Cd through the soil profile and had toxic effects on test plants and soil microorganism

•

Phosphate compounds Phosphate compounds enhance the immobilization of metals in soils through various processes including: direct metal adsorption by P compounds, phosphate anion-induced metal adsorption, and precipitation of metals with solution P as metal phosphates

Depending on the source, soil application of P compounds can cause direct adsorption of metals onto these compounds through increased surface charge and enhanced anioninduced metal adsorption. Metal adsorption onto apatite is facilitated through the exchange of Ca2+ from the apatite particle with the metal cations in soil solution

•Liming materials •

These include calcite (CaCO3), burnt lime (CaO), slaked lime (Ca(OH)2), dolomit(CaMg(CO3)2)and slag (CaSiO3). The acidneutralizing value of liming materials is expressed in terms of calcium carbonate equivalent (CCE), expressed as a weight percentage of pure CaCO3.Liming, as part of normal cultural practices, has often been shown to reduce the concentration of Cd, Pb and other metals in edible parts of crops. Similarly, liming serpentine soils containing toxic levels of Ni has been shown to alleviate the phytotoxic effects of Ni. In these cases, the effect of liming materials in decreasing metal uptake by plants has been attributed both to decreased mobility in soils (through adsorption/precipitation) and to the competition between Ca2+ and metals ions on the root surface.

Organic composts • The major sources of organic composts include biosolid and animal manures livestock manure and other organic wastes, especially when they are composted in the presence of sewage sludge Most manure products contain low levels of heavy metals (except Cu and Zn in swine manure and As in poultry manure).

 Manure byproducts that are low in metal content can be used to immobilize metal contaminants in soils

CONCLUSION OF SOME RESEARCHES

POLLUTION OF SOIL BY AGRICULTURAL AND INDUSTRIAL WASTE

• After 30 - 40 years of intensive use of fertilizer in lowland areas of West Java, including rock phosphate, the concentration in the soil of heavy metals such as lead and cadmium still remains below toxic levels. However, these elements are sometimes present naturally in rock phosphate, so that continuous monitoring is needed. • The results showed that vetiver grass could grow well on soils contaminated with high concentrations of lead and cadmium. By concentrating the contaminants in its roots, the vetiver grass reduced the concentration of lead in soil by as much as 38 - 60%, and cadmium by 35 - 42%.

RELATIONSHIP BETWEEN HEAVY METAL CONCENTRATION IN SOILS OFTIAWAN AND UPTAKE BY CROPS There is no clear relationship between the concentration of cadmium in brown rice, and the amount of cadmium extracted from the soil by 0.1 M HCl. This means that the 0.1 M HCl extraction method is not suitable for predicting the uptake of soil cadmium and its presence in rice grain. Exchangeable (or available) forms of cadmium and lead can be transformed into unavailable forms if the soil is amended with manganese oxide, calcium carbonate or zeolite. The concentration of cadmium in the soil solution, and levels of cadmium extracted by DTPA and EDTA, decreased significantly when the soil was treated with calcium carbonate. Treatments of zinc oxide, however, had no significant effect.

REFERENCES

1.Chaney, R.L., S.L. Brown, J.S. Angle, T.I. Stuczynski, W.L. Daniels, C.L. Henry, G. Siebielec, Y.M. Li, M. Malik, J.A. Ryan and H. Compton. 2000. In situ Remediation/ Reclamation/Restoration of Metals Contaminated Soils using Tailor-Made Biosolids Mixtures. In Proc Symposium on Mining, Forest and Land Restoration: The Successful Use of Residuals/Biosolids /Organic Matter for Reclamation Activities (Denver, CO, July 17-20, 2000). Rocky Mountain Water Environment Association, Denver, CO

2. Diah Setyorini, Tini Prihatini and Undang Kurnia,2002 .POLLUTION OF SOIL BY AGRICULTURAL AND INDUSTRIAL WASTE. Centre for Soil and Agroclimate Research and Development, Jalan Ir. Juanda No. 98 Bogor 16123, Indonesia 3.Joonki yoon,2005. PHOSPHATE-INDUCED LEAD IMMOBILIZATION IN CONTAMINATED SOIL . A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE 4. Nanthi S. Bolan Santiago Mahimairaja and Julien Lefeuvre,2003. Remediation of

heavy-metal contaminated soils –to mobilize or immobilize?. Institute of Natural Resources, Massey University, and Marseille University, France. New Zealand Science Review Vol 60 (4) 2003

5. Zueng-Sang Chen,2000. relationship between Heavy Metal Concentrations in Soils of Taiwan and Uptake by Crops. Department of Agricultural Chemistry National Taiwan University Taipei Taiwan, ROC, 2000-03-01 106

Thank you for your attention