Removal of arsenic from groundwater using adsorption to ferrihydrite-coated laterite in Burkina Faso

Abstract: In several parts of Burkina Faso, there is an urgent need of making arsenic contaminated water potable. The shallow, dug out wells traditionally used in the rural areas provides small, inconsistent yields and are vulnerable to microbes. Consequentially, many of them have now been replaced with drilled tube-wells, intercepting water from fractures in the bedrock and providing reliable water sources. However, as arsenic is naturally present in the bedrock in many parts of the country, previous studies has shown that water from a lot of these wells is not safe to drink. In some cases, the wells had to be closed due to high arsenic concentrations. The medical effect of the arsenic exposure has also been evaluated among the inhabitants of affected villages, indicating that the problem is critical. Previous studies in this project were focused on using the commercial material Granular Ferric Hydroxide (GFH) as a possible method for arsenic removal in the villages. As the price of GFH however is too high, other methods has been researched instead. In this study, natural laterite rock has been crushed and used as adsorbent in column experiments, but indicating a low arsenic capacity. The same lateritic sand has then been coated in ferrihydrite both by drying the materials together in the oven and by a centrifugation method previously evaluated in Uppsala, Sweden. Although results after the ferrihydrite-coating improved, the adsorption capacity was still significantly lower than that of GFH. The results from the ferrihydrite-coated sand also differed largely from those previously found in Uppsala, and though this could be due to the fact that this study was made with natural water instead, it is thought that the inevitable alterations in the coating method might have affected the result of the coating to a great extent. The conclusion of this study is therefore that ferrihydrite-coated sand still is a possible low-cost adsorbent material for arsenic contaminated water in developing countries, though factors such as sand material, grain size and coating method should be evaluated further.