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Hernell, Anna (2009) Water purification capacity of natural mixed clays from Malawi. Other thesis, SLU.

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Lack of fresh and clean drinking water is a problematic issue for many people worldwide. The water quality in some streams in Malawi, situated in south east Africa, has recently been investigated. The study shows that the concentration of several heavy metals exceeds the guideline values in drinking water set by WHO. Even though some heavy metals are essential for human beings in low concentrations, they are hazardous to health in high concentrations. Problems with contaminated water exist all over the world but are striking and more difficult to solve in countries with low financial assets. It is therefore of great importance to find an effective technique to purify water that is both simple and cheap and where preferably domestic material is used. The aim of this study is to investigate whether three natural mixed clays from Malawi can be used to purify contaminated water from the heavy metals chromium(III), lead(II), cadmium(II), copper(II) and zinc(II) through adsorption. X-ray powder diffraction analyses proved that all samples contained quartz, and indicated presence of the iron oxide hematite. The chemical content of the samples was determined with a scanning electron microscope. Acid and base titrations were thereafter performed on raw material as well as on clay that had been purified from organic matter, carbonates and iron compounds, to obtain information regarding the chemical properties of the clay minerals. Finally, adsorption experiments were carried out by mixing the clays with heavy metal solutions and study the adsorption as function of pH. The pH values of the investigated clays are naturally high, which promotes hydrolyses of chromium(III) and lead(II) to precipitate and get sorbed on the surface. Cadmium(II), copper(II) and zinc(II) form on the contrary surface complexes, mainly inner-sphere ones. The adsorption of chromium(III), lead(II) and copper(II) was complete at pH = 7 for the purified clays, whereas cadmium(II) and zinc(II) were adsorbed to only 77 and 75 %, respectively, at pH ≈ 7.5. However, all metals are in principle completely removed from the aqueous phase in the raw material, which indicates that these nontreated natural clays are highly potential in heavy metal removal.

Item Type: Thesis (Other)
Keywords: chromium(III), lead(II), zinc(II), copper(II), cadmium(II), adsorption, surface complex, natural clays, water treatment
Subject (faculty): Faculty of Veterinary Medicine and Animal Science > Dept. of Soil and Environment
Divisions: SLU > Faculty of Natural Resources and Agricultural Sciences
Depositing User: Gertrud Nordlander
Date Deposited: 06 Nov 2009
Last Modified: 18 Aug 2015 10:17
URI: http://ex-epsilon.slu.se/id/eprint/3434

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