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Arsenic Removal Efficiencies of a Few Impregnated Silicate Meterials

M. F. Islam
Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Bangladesh

M. Mokhlesur Rahman
Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Bangladesh

Abstract/ Executive Summary:

The commonly available brick particles were impregnated with selected compounds and tested for As absorption properties. The materials tested are FeSO₄ treated roasted brick particles, Fe₂(SO₄)₃ treated roasted brick particles, FeSO₄ and Na₂CO₃ treated brick particles, Fe₂(SO₄)₃ and Na₂CO₃ treated brick particles, ZnSO₄ and Na₂CO₃ treated brick particles, FeSO₄ and Na2HPO₄ treated brick particles and waste cement plaster as such. It was observed that the substances showed different behavior of As absorption on short and long time contact. On long time contact periods the absorption capacities are much increased with high concentrations of As in solution. However with short time contact with low As concentration, the materials show saturation or no absorption after certain time period. Thus variable capacities for As absorption are shown depending on concentration, time of absorption and interval time between two contact periods. As (III) absorption was studied in the pH range 2.45-7.0. The data also show that with a contact time of 3 hrs. or more, the level of As is reduced to the acceptable limit of 0.05 ppm in water. High concentration of phosphate in water decreases as absorption as phosphate is also strongly absorbed by iron oxide impregnated brick particles. Leaching of loaded arsenic from brick particles using different common chemicals was also studied for ferrous sulfate treated roasted brick particles. Out of the solutions of common chemicals (10% caustic soda, 20% sodium chloride, 10% sodium carbonate, 10% potassium dihydrogen phosphate, 10% TSP and 5% NH₃) only 10% caustic soda can leach ~ 95% As from As loaded brick particles and others much less. Ordinary water within pH 4-7 leach very little arsenic from iron oxide impregnated brick particles.

Keywords: Cheap materials, Arsenic filters, Poor.

Location: Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Arsenic

Objectives:

The purpose of the work was to identify very cheap materials for the making of arsenic filters for the poor.

Methodology:

For this investigation, ordinary locally made bricks properly burned (first class bricks) and old waste cement plaster were collected and used for study. At first these materials were crushed into small sizes. Of which only (-3.15+2) mm mesh and (-2+0.2) mm mesh sizes were taken for experiments. Then the fixed sized crushed bricks and waste silicate materials were treated by the following methods. The chemicals used for treatment are ferruos sulfate, ferric sulfate, zinc sulfate, disodium hydrogen phosphate, sodium carbonate etc. a) FeSO₄ treated roasted brick particles 200 g crushed brick particles were soaked with freshly prepared 20 % FeSO₄ solution for 24 hours. 250 ml solution was used for 200 g crushed brick. Then the FeSO₄ impregnated wet crushed brick particles were taken in a clay pot for heat-treatment in a make shift furnace after draining out excess solution. In this experiment an electric heater of 2 Kw was used whose surrounding was closed by brick walls with clay as mortar to minimize the loss of heat. A thermometer was used to record the temperature. Soaked crushed brick was heated for three hours at around 450^OC-500^OC, FeSO₄ being converted to oxides of iron. This iron oxide impregnated brick particles were used for investigation. The thermal decomposition reaction of ferrous sulfate is well known. b) FeSO₄ and Na₂CO₃ treated brick particles 200 g crushed brick particles were soaked with freshly prepared 250 ml. of 10% FeSO₄ solution for 24 hours and filtered in order to drain out the excess FeSO4 solution and soaked brick particles were dried in the sun. Then the dried 10% FeSO₄ soaked brick particles were again soaked with 250 ml. of 10% Na₂CO₃ solution for 24 hours. Then the brick particles were filtered, washed free of sulfate and dried in the sun. Hydrated ferric and ferrous oxides are formed by the decomposition of unstable ferrous carbonate. c) Fe₂(SO₄)₃ treated roasted brick particles 200 g crushed brick particles were soaked with 250 ml. of 10% Fe₂(SO4)₃ solution for 24 hours and filtered, and dried. It was then heated for an hour and a half using the same electric make shift furnace at temperatures ~ 450^OC. The impregnated brick particles were used for subsequent study. The decomposition of hydrated ferric sulfate is also a well known reaction.d) ZnSO₄ and Na₂CO₃ treated brick particles 200 g crushed brick particles were soaked with 250 ml. of 10% ZnSO₄ solution for 24 hours and then filtered, and dried in the sun. Then the 10% ZnSO₄ soaked dried brick particles were soaked with 250 ml. of 10% Na₂CO₃ solution for 24 hours and then filtered, washed free of sulfate and dried in the sun. The basic zinc carbonate is formed insitu by the reaction. ZnSO₄ + Na₂CO₃ + H₂O ZnCO₃ . 2 Zn(OH)₂ . H₂O + Na₂SO₄. e) Fe₂(SO₄)₃ and Na₂CO₃ treated brick particles 200 g crushed brick particles were soaked with 250 ml. of 10% Fe₂(SO₄)₃ solution for 24 hours and then filtered, and dried in the sun. Then the 10 % Fe₂(SO4)₃ soaked brick particles were soaked with 10 % Na₂CO₃ solution for 24 hours then filtered, washed free of sulfate and dried in the sun and collected. The hydrated ferric oxide is formed. f) FeSO₄ and Na₂HPO₄ treated brick particles 200 g crushed brick particles were soaked with 250 ml. of 10% FeSO₄ solution for 24 hours and then filtered and dried in the sun. Then the 10% FeSO₄ soaked brick particles were again soaked with 250 ml. of 10% Na₂HPO₄ solution for 24 hours and then filtered, washed free of sulfate and dried in the sun. Ferrous phosphate is formed insitu by double decomposition.

Source of Information: Bangladesh J. Sci. Ind. Res. 41(1-2), 1-14, 2006

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The experimental data show that the impregnated brick particles and sand-cement composites have excellent arsenic absorption properties from water. Ordinary bricks and cement are in effect silicate materials manufactured from clay. Impregnation with non toxic iron and zinc compounds enhances the arsenic absorption properties of brick particles. However the iron oxide impregnation may be a cheaper process than that with zinc oxide. It seems higher iron oxide percentage favor more As (III) absorption. As (V) absorption is expected to be more favorable as literature reports better removal with other iron containing materials for the higher oxidation state of arsenic. Besides the arsenic absorption capacity the kinetics of absorption and leaching characteristics suggest the suitability of iron oxide impregnated materials for practical filters. The other impregnated materials have to be studied more for practical use. The chemistry of the arsenic absorption process remains to be investigated. However a chemisorptions mechanism is more likely for iron oxide impregnated brick materials in view of the difficult leaching of arsenic from the arsenic loaded material.

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