Removal of heavy metals from industrial wastewaters using natural adsorbents

Abstract

The use of readily available natural materials as adsorbents of heavy metals from industrial wastewaters was investigated. The natural materials investigated were bagasse, paddy husk, corn cob, wheat bran, peanut skin, and human hair. Two modes of removal were carried out. In one set of experiments, effluents from different industries were run through columns packed with natural adsorbents. In the other set, the effluents were simply agitated with known weights of the natural adsorbents. Heavy metal concentrations of the industrial effluents were determined before and after contact with the natural adsorbents using atomic absorption spectroscopy. Parameters such as column height, substrate weight, particle size of the substrate, and the pH of the substrate in solution were varied to obtain optimum conditions for heavy metal removal. Virtually all the materials were found to be good scavengers of heavy metals, comparable to the conventional, expensive commercial materials such as ion-exchange resins commonly used for wastewater treatment. The mechanism of removal is proposed to be similar to ion-exchange resins and adsorption. The adsorption capacities of the natural adsorbents vary from one heavy metal to another. Based on the overall mean percentage removal of heavy metals (87.6–92.2%), the heavy metal adsorbing capacity of the natural adsorbents is of the order: corn cob > paddy husk > peanut skin > human hair > wheat bran > bagasse. In terms of heavy metal adsorbed per unit weight of adsorbent, the efficiency of heavy metal scavenging is of the following order: bagasse and human hair > corn cob and peanut skin > wheat bran > paddy husk. Efficiency of heavy metal removal by the natural adsorbents increases with column height and decreases with particle size of adsorbent and residual heavy metal concentration in the effluent. In view of its efficiency, simplicity, low cost, and reliability, this technique has very good potential for heavy metals removal from high-volume industrial wastewaters.