REMOVAL OF ARSENIC FROM AQUEOUS SOLUTION BY ADSORPTION WITH ACTIVATED CARBON GROUP MEMBERS: Ajit Singh Patel Kuldeep Singh Reyad Ranjon Roy

BACKGROUND AND OBJECTIVE: BACKGROUND:  Sources of arsenic  Why is its removal necessary?  Methods for removal OBJECTIVE:  Removal of arsenic upto permissible limit.  Comparison of adsorption parameters  Study the effect of modification, pH, temperature and presence of co-ions.  Selection of efficient and economic method

METHODS: The following types of activated carbon were used for :  Adsorption capacity and Isotherm study  Kinetic study  pH change, temperature variation, presence of co-ions  Coal derived activated carbon modified with NZVI  Bituminous based, coconut coal and wood based activated carbon  apricot stone based activated carbon hybrid adsorbents  Activated carbons with iron hydro(oxide) nanoparticles  Biomass waste (bean pods) derived activated carbon  china calgon activated carbon  Darco and norrit activated carbon  Charcoal activated carbon  Activated carbon from fibre cloths  Activated carbon from pine wood sawdust

FINDINGS:  modification of AC by iron gives higher removal and reduction in regeneration frequency.  rapid adsorption and better removal efficiency by modification with Fe +3 than Fe +2.  amount of iron present in water affects adsorption capacity as when amount of Fe increases from 0 to 4.22% only then removal efficiency increases.  Oxidised AC gives very rapid and efficient removal upto less than 10 microgram/L As content.  the activated carbon, with higher value of ash content, was more effective in removing As(V).  Biomass(bean pods) derived AC provides very cheap removal of As(III). This type of AC have higher efficiency than other for same specific Area.

 Generally maximum adsorption capacity is found between pH 6-8,but bituminous waste and coconut husk based AC gives maximum adsorption capacity at pH 11.  coal derived AC which is modified with NZVI particles is superior for removal of As(III) in available pH conditions for natural water.  Charcoal based AC is found to be best for the removal of As(V) in pH range from 6 to 8.  SO 4 2- and Cl - have more affinity to AC than arsenic.  Presence of common divalent cation like Mg +2,Ca +2 and Fe +2 increases the removal % of arsenate whereas presence of Ag + and Cu + increases the removal % of As(III) but decreases the removal % of As(V) considerably.  Adsorption by Fe +2 modified AC is endothermic while Adsorption by Fe +3 modified AC is found exothermic in case of apricot based AC. Some AC shows insignificant change in adsorption capacity with temperature variation.

Issues and directions for further research  For economic new waste produced materials such as from nutshell, peat etc. should be used for the production of AC.  New modification method should introduce because Modified activated carbon has more adsorption capacity than virgin activated carbon.

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