Development of Alumina Modified Laterite Material for Fluoride Removal from Contaminated Water

Fluoride in groundwater is a threat to the provision of potable water to our rural communities because continuous consumption of water contaminated with fluoride could lead to dental fluorosis or even in extreme cases, skeletal fluorosis. Many fluoride removal techniques have been suggested but most of them have been found not to be practical and sustainable in Ghana as they are either expensive or need highly skilled personnel to operate. The need for a local adsorbent which is less expensive and effective for fluoride removal is of much relevance. Laterite has been identified as a local adsorbent which is readily available and not expensive. However, there have been debates among researchers about the effectiveness of laterite to remove fluoride. This study investigated the characteristics of three (3) laterites from three locations of the Upper East Region for fluoride removal. These areas are Agamolga, Balungu and Dua. Chemical and mineralogical analyses performed using X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) methods showed varying amounts of iron oxide/hydroxide (goethite/hematite), silica and kaolinite. Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray (EDX) showed that the minerals are intimately associated. Isoelectronic Point (IEP) value was influenced by the mineral composition with the larger IEP value corresponding to higher iron oxide/hydroxide content. The study measured the responses of the different laterites to fluoride uptake under different conditions of pH, temperature, particle size of adsorbent and initial concentration of fluoride solution. The responses showed that Agamolga and Balungu laterites could remove fluoride better than Dua laterite mainly due to the chemical and mineralogical constituents of these two laterites as compared to Dua laterite which has high silica content. To improve the adsorption capacity of the iv laterite for fluoride uptake, an alumina modified laterite (AML) was developed using Balungu laterite. The effect of treatment temperature and application to different conditions of fluoride uptake was investigated including adsorbent dosage, initial fluoride concentrations, solution pH and fluoride uptake in the presence of other competing anions. The response of AML to the different experimental conditions shows that the material is capable of removing fluoride to a level below the WHO recommended limit of 1.5 mg/L. At a dosage of 4% solids, AML could remove fluoride from 10±0.2 to 0.42 mg/L without any pH adjustment within 35 minutes. The results indicated that the adsorption characteristics of AML were not significantly affected in the pH range of 6-9 and this means pH adjustment of the raw water is unnecessary. The results also showed that there was an improvement on the adsorption capacity as the raw laterite assumed an adsorption capacity of 0.55 mg/g whereas the AML material assumed a value of 0.69 mg/g. The results also showed little or no significant change in fluoride adsorption by AML in the presence of other competing ions such as chloride, sulphate, phosphate, bicarbonate and nitrates.

Source: KNUST