Adsorbent Materials From Rice Husks And Water Hyacinth Ashes Blended With Bone Char For Removal Of Fluoride Ions From Contaminated Water

ABSTRACT

Safe and readily available water is important for public health, whether it is used for drinking, domestic use, food production or recreational purposes. Consumption of contaminated water may lead to acute and chronic health effects. The most common water pollutants include heavy metals, pesticides, and anions such as fluorides, arsenic, arsenite, chromate and selenate, which cause various diseases such as brain, liver and bone ailments. Among the pollutants, fluoride is the most occurring contaminant in water. Fluoride ions are absorbed by the body mainly through drinking water containing a concentration of more than 1.5 mg/L for a long period of time. At high levels, they cause health problems which range from mild to severe teeth and bone fluorosis. Many methods have been used for removal of anionic contaminants such as fluoride from drinking water. These methods include reverse osmosis, precipitation, electro dialysis and adsorption. Most of these methods are too expensive. This study aimed at synthesizing an adsorbent material from low cost agricultural waste products materials namely water hyacinth ash (WHA) and rice husks ash (RHA) blended with bone char and determine its effectiveness in removal of fluoride ions from contaminated water. Five zeolitic materials were prepared and labelled as zeolitic A (ZA), zeolitic B (ZB), zeolitic C (ZC), black bone char (BBC) and white bone char (WBC) by varying the amounts of rice husks and the water hyacinth ashes and blending with white and black char. Analysis of various oxides contained in the adsorbents was done by X-ray Fluorescence Spectrometer (XRF). Adsorption tests for fluoride ions by the five adsorbents were carried out based on the batch adsorption studies. These include varying the shaking speed, temperature, contact time, initial anion concentration and adsorbent dose. The concentration of fluoride ions remaining in the solution after adsorption was analysed using Fluoride Ion Selective Electrode (FISE). Results for the adsorption capacities for the five adsorbents fitted best onto Freundlich isotherm model which gave adsorption capacity (Kf) values as follows; ZA 1.181, ZB 1.281, ZC 1.061, BBC 1.142, BWC 1.112. The zeolite B had the highest adsorption capacity. This indicates that blending a zeolitic material by black bone char improves its adsorption capacity for fluoride ions from contaminated water. At optimum concentration of fluoride ion and optimum temperature, ZB removes 75.50% and 80.00% of the ion respectively. It gives 75.50% at a shaking speed of 120 rpm and 77.00% at optimum contact time. Therefore it is necessary to optimize use of locally available materials for application in defluoridation of water.