Water purification capacity of natural mixed clays from Malawi
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 drink...
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| Formato: | Otro |
| Lenguaje: | sueco Inglés |
| Publicado: |
2009
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| Materias: | |
| Acceso en línea: | https://stud.epsilon.slu.se/12353/ |
| Sumario: | 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. |
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