DEVELOPMENT OF ADSORBENTS FOR SIMULTANEOUS REMOVAL OF ARSENIC AND FLUORIDE FROM DRINKING WATER

Abstract

Water pollution by arsenic and fluoride has been of a serious concern worldwide particularly in INDIA. It has been proved by researchers that excess intake of fluoride causes serious problem such as dental decay, fluorosis, skeleton fluorosis, fatal cerebral function and neurotransmitters etc. In similar fashion if arsenic is present in drinking water then it may cause harm-full effects to human health that ranges from acute lethality to chronic and carcinogenic effects etc. In order to control the effects various technologies have been developed worldwide. Researchers and technologist are trying their best to find out a solution to these problems through ecofriendly and economical methods. Amongst the various technologies developed, Adsorption using nanoparticles on a host material (Ion exchange resins) is one of the best suited techniques for the simultaneous removal of arsenic and fluoride. But metal and metal oxide nanoparticles, because of their small size and high reactivity, in many cases are not so chemically stable and show lack of enough mechanical strength. They also exhibit extremely high pressure drop or head loss when they are used in fixed-bed column operation. Also, nanoparticles have a natural tendency to agglomerate under the influence of van Der Waal's force and once this happens, their surface area to volume ratio gets reduced and subsequently their effectiveness for the intended use gets reduced. In this study a polymer supported hybrid nano-adsorbent has been developed. Weak base anion exchanger resin has been synthesized by dispersing hydroxyapatite or zirconium nanoparticles and ILFO nanoparticles with the help of HCl, zirconium, NaOI1, NaCl and FeC13. Synthesized material can be named as Modified IRA-67. Purolite's weak base anion exchanger has been used as host material. This polymer supported hybrid nano-adsorbent can provide synergy for simultaneous removal of fluoride and arsenic. Column study revealed that fluoride can be easily removed well below permissible limit i.e. 1.5mg/I from 6.8mg/I up to 80 bed volumes and same adsorbent and it can be easily regenerated by 30 bed volumes by using cheaply available innocuous chemicals. Noticeable thing is that it does not loses its adsorption capacity as in case - of all the synthetic water run i.e. first run, second run and in even third run its adsorption capacity was almost same i.e. 80 bed volumes. Modified lRA-67 can also be used for simultaneous removal of arsenic also up to 3600 bed volumes well below the permissible limit iv i.e. 10 ppb from 200ppb which is synthetic influent concentration and breakthrough occurs at 11000 bed volumes. In this study a new polymer supported hybrid nano-composite Modifed IRA-67 was fabricated by impregnating (ZrOCl2*8H20 + 1-ICI) & (NaCI + NaO1-1) through column run and after that through batch by passing (FeCl3 + NaOH) on to a porous weak base anion exchanger resin provided by PUROLITE. Weak base anion exchanger provided by PIJROLITE was selected as a host material mainly because of the potential donnan membrane effect exerted by the immobilized positively charged amine groups bound to the polymeric matrix, which would result in pre-concentration and permeation enhancement of fluoride prior to their effective sequestration by the impregnated nanoparticles. Modified IRA-67 shows highly selective fluoride and arsenic removal from drinking water in the presence of competing ions such as I-1CO3 , S042 & Cl- at very high concentration comparatively to target toxic metal. Fixed-bed column adsorption of a simulated water indicated that fluoride removal from drinking water resulted in decrease of the toxic metal from 6.4mg/I tol.5mg/l (drinking water permissible limit - recommended by WI-b). The exhausted adsorbent bed is acquiescent to efficient regeneration by NaCl and NaO1l for the repeated use. Although Modified IRA-67 loses its adsorbing capacity - after certain regeneration cycles but not after second regeneration as mentioned in following studies, that's why it is good adsorbent. Fluoride adsorption on Modified IRA-67 was dependent on solution p1-I due to ion-exchange nature and it can be validated by freundlich and Langmuir isotherm model.