Competitive adsorption between arsenic and fluoride from binary mixture on chemically treated laterite

Abstract

The present paper deals with individual as well as simultaneous removal of arsenic and fluoride from synthetic water using acid-base treated laterite in batch mode along with management of the spent adsorbent. Optimum conditions for maximum removal of both arsenic and fluoride in single component system are found as pH 5, adsorbent dose 20gL−1, contact time 300min with initial concentration of arsenic and fluoride as 500μgL−1 and 10000μgL−1 respectively. Adsorption isotherm data fitted well to Langmuir model and under the optimum conditions the Langmuir adsorption capacity of present adsorbent is found to be 769μgg−1 for arsenic and 526μgg−1 for fluoride. Single component adsorption followed Pseudo 2nd order kinetics. The binary adsorption experiments were performed at the same optimum conditions with varying concentrations of arsenic and fluoride. The combined adsorptions of arsenic in binary systems do not differ much, while fluoride shows antagonistic behavior. The extended Freundlich model is found to best represent the apparent equilibrium adsorption phenomena in binary system. The present adsorbent is able to simultaneously reduce the arsenic and fluoride concentration below permissible limits of USEPA drinking water standards. Solidification technique was used for the management of the spent adsorbent by its immobilization in form of a clay brick. Leaching test results revealed that leaching of arsenic and fluoride from the spent adsorbent is well below the permissible limits as per the USEPA norms.