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REMOVAL OF ARSENIC FROM GROUNDWATER USING DOLOMITIC SORBENTS Project QUB20/08/11 Yousef Salameh Dr G. Walker, Dr. M. Ahmad and Prof. S. Allen School of Chemistry and Chemical Engineering Queen’s University Belfast. Presentation Overview. Objectives Introduction Materials and Methods

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  1. REMOVAL OF ARSENIC FROM GROUNDWATER USING DOLOMITIC SORBENTSProject QUB20/08/11 Yousef Salameh Dr G. Walker, Dr. M. Ahmad and Prof. S. AllenSchool of Chemistry and Chemical EngineeringQueen’s University Belfast

  2. Presentation Overview Objectives Introduction Materials and Methods Results Project progress Future work 2 Chemistry and Chemical Engineering QUB

  3. 3 Project Objectives • An investigation to ascertain the optimum conditions for thermal and chemical treatment of the dolomite in order to achieve maximum removal of arsenic species. • Assess the efficiency of the raw and the modified dolomite as adsorbents for the As(V) and As(III). • Evaluation of the sorption behaviour of As(V) and As(III) onto raw and modified dolomite by conducting equilibrium isotherms. • Removing As(V) and As(III) under flow conditions (column studies). Chemistry and Chemical Engineering QUB

  4. Introduction Arsenic presents in aquatic environments mostly in inorganic species, arsenate and arsenite. Arsenate, As (V), is the predominant arsenic form found under aerobic and oxidizing conditions. Arsenite, As (III), occurs mainly in anaerobic and reducing conditions. Arsenite is considered more toxic than arsenate and tends to be more mobile in the aqueous environment. 4 Chemistry and Chemical Engineering QUB

  5. 5 Introduction Research focussing on studying new sorbent materials for the removal of arsenic from aqueous. Many areas in the world still require an appropriate technology, which is inexpensive, simple to use and easily applied. The operational cost for adsorbents is mainly related to optimising the capacity and adsorption kinetics. Chemistry and Chemical Engineering QUB

  6. 6 Arsenic problems in Bangladesh Chemistry and Chemical Engineering QUB

  7. Arsenic removal from drinking water Coagulation Ion exchange Reverse osmosis Liquid-liquid extraction Adsorption 7 Chemistry and Chemical Engineering QUB

  8. The Dolomite Group of Minerals The Dolomite is considered a promising low cost adsorbent. It is composed of minerals with an unusual trigonal bar 3 symmetry. The general formula of this group is AB(CO3)2, where A can be either calcium, barium and/or strontium and the B can be either iron, magnesium, zinc and/or manganese. The amount of calcium and magnesium in most specimens is equal, but occasionally one element may have a slightly greater presence than the other. Small amounts of iron and manganese are sometimes also present. 8 Chemistry and Chemical Engineering QUB

  9. Experimental Materials The dolomite used in this study was mined from a deposit in Co. Fermanagh, Northern Ireland. The typical chemical composition of the dolomite in the deposit was 44% MgCO3 and 53% CaCO3. The surface area was found to be 17.36(m2g-1) for particle size 1.0-1.2 mm. 9 Chemistry and Chemical Engineering QUB

  10. Experimental Methods 10 • The dolomite was charred at the following temperatures 600oC,700oC and 800oC. • Equilibrium experiments were carried out using 0.05 + 0.0005g of the dolomite which was contacted with 50 ml of arsenic solution. • Appropriate dilutions were made to give a range of arsenic • concentrations. The samples were placed in glass jars and • subsequently capped and shaken in a mechanical shaker for • 5 days at 80 rpm. • Samples of the aqueous phase were taken at regular intervals and then were filtered and prepared for analyses using ICP-AES. • Duplicate samples were measured and standard error in the readings was less than 3%. Chemistry and Chemical Engineering QUB

  11. 11 The effect of pH on As (V) removal Adsorbent dose: 1g/L; Adsorbent particle size: 0.7-2.0 mm; Initial arsenic concentration: 500 ppb; contact time: 5 days

  12. 12 The effect of adsorbent mass on As(V) removal Volume of test solution: 50 ml; pH 2; contact time: 5 days

  13. 13 The effect of adsorbent particle size on As(V) removal Volume of test solution: 50 ml; pH 2; contact time: 5 days.

  14. 14 As(V) adsorption equilibrium models • Langmuir and Freundlich mathematical models Chemistry and Chemical Engineering QUB

  15. 15 As(V) adsorption kinetics Volume: 250 ml; pH 7; Adsorbent dose: 1g/L..

  16. 16 As(V) adsorption kinetics: 1st order reaction model ln(qe − qt) = ln qe − K1ads t

  17. 17 As(V) adsorption kinetics: 2nd order reaction model

  18. 18 As(V) adsorption kinetics: Thermodynamic modelling

  19. 19 As(V) adsorption kinetics: Ca/Mg dissolution

  20. 20 As(V) adsorption kinetics: Ca/Mg dissolution The dolomite dissociates under certain thermal conditions to give: CaMg(CO3)2 → CaCO3 + MgO + CO2 and with further treatment CaCO3 → CaO + CO2 The formation of MgCO3 and CaCO3 allows the formation of arsenic oxide and arsenic carbonate, so precipitation of these compounds will take place and thus the arsenic removal will increase. Chemistry and Chemical Engineering QUB

  21. 21 Charred dolomite: effect of pH on As(V) removal The pH dependence of As(V) adsorption on 8 hours charred dolomite (for different charring temperatures). Adsorbent dose: 1g/L; Initial arsenic concentration: 500 ppb; contact time: 5 days.

  22. 22 Charred dolomite: effect of pH on As(III) removal The pH dependence of As(III) adsorption on 8 hours charred dolomite (for different charring temperatures). Adsorbent dose: 1g/L; Initial arsenic concentration: 500 ppb; contact time: 5 days.

  23. Project progress Isotherm and kinetic studies were conducted on the raw dolomite in order to assess its efficiency as adsorbent for the arsenic. Raw dolomite requires acidic solutions and it does not remove As (III). The dolomite was charred at the following temperatures 600oC, 700oC and 800oC for 1, 2, 4 and 8 hours. Charred dolomite showed excellent removal of As(III) and As(V) of a wide range of initial pH 23 Chemistry and Chemical Engineering QUB

  24. Isotherm experiments were carried out on charred dolomite at various initial pH. 8 hours, 700oC and neutral pH (initial solution) was chosen as the optimum conditions. Equilibrium investigations on this charred dolomite have been undertaken to determine the full potential of this dolomite as a potential adsorbent. Comparisons of charred dolomite with commercial adsorbents have been undertaken. 24 Project progress Chemistry and Chemical Engineering QUB

  25. Future work Further equilibrium, kinetic and thermodynamic investigations on (8 hours 700oC charred dolomite) will be undertaken. Column studies will be carried out to assess its efficiency under flow conditions. Desorption studies Further chemical treatment to the raw dolomite to achieve the maximum removal of arsenic species 25 Chemistry and Chemical Engineering QUB

  26. REMOVAL OF ARSENIC FROM GROUNDWATER USING DOLOMITIC SORBENTSProject QUB20/08/11 Yousef Salameh Dr G. Walker, Dr. M. Ahmad and Prof. S. AllenSchool of Chemistry and Chemical EngineeringQueen’s University Belfast

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