doi:10.1038/nindia.2016.56 Published online 26 April 2016
Researchers have developed a natural, soil-based adsorbent that can remove harmful elements such as arsenic and fluoride from aqueous solutions1, making it potentially useful for removing these elements from drinking water.
Long-term exposure to arsenic can cause various cancers, while excess fluoride in potable water causes fluorosis, which deforms bone and teeth. Current techniques for removing arsenic and fluoride are complex and expensive.
To devise a simple, low-cost method for removing arsenic and fluoride, the researchers synthesized an adsorbent by treating laterite soil with an acid and a base, which increased both the surface area and porosity of the soil.
Increasing the adsorbent’s concentration enhanced its efficiency to remove arsenic and fluoride from aqueous solutions. At a concentration of 20 grams per litre, the adsorbent removed 92% of arsenic and 78% of fluoride.
Arsenic removal varied little with pH, whereas fluoride removal increased with decreasing pH of solutions. At a low pH, electrostatic attractions between the adsorbent and fluoride ions facilitated fluoride removal since the adsorbent’s surface is negatively charged while fluoride is present as negatively charged ions in solution.
Both arsenic and fluoride removal increased up to 5 hours, after which they remained almost constant. In addition, negligible amounts of adsorbed arsenic and fluoride leached from the adsorbent, suggesting that this method is eco-friendly, the researchers say.