Remediation of turbid water containing lead and cadmium ionsusing zeotype materials derived from rice husks and water hyacinth ashes
Ngugi, Hellen Wambui
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Water scarcity problem is of great concern globally especially in developing countries including Kenya which has per capita available water of 650 m3 per year as opposed to the recommended 1700 m due to rapid growth in population, industrialization and pollution a situation likely to worsen if drastic deliberate measures are not taken. Common water pollutants include pesticides, sewage, heavy metals and suspended particles. Lead and cadmium are among the most prevalent heavy metal contaminants due to their extensive uses in batteries, paints, fertilizers and pesticides. These heavy metals are absorbed by the body mainly through intake of food and water and at high levels bioaccumulate causing health problems which range from less severe cases of stomach upsets to more severe cases of damage of brain and the nervous system. Although several water treatment materials are available in the market they are expensive and inaccessible to many. There is need for continued search for alternative adsorbents that are locally available and accessible to the poor majority. The current study was geared towards synthesis of zeotype material, an adsorbent, and determination of its effectiveness in removal of heavy metal ions and turbidity from contaminated water. Four zeolitic blends were synthesized using the ashes from rice husk waste as the source of silica and fast growing water hyacinth ash as the base. The different zeotype materials were obtained by varying the ratio of water hyacinth ash while keeping that of rice husk ash constant. Batch sorption studies were done at various conditions of contact time, pH , temperature, shaking speed, adsorbent dose and concentration of the metal ion in solution and the data obtained was fitted in the Freundlich and Langmuir adsorption models to obtain adsorption capacities. Data for adsorption of both lead and cadmium ions on the zeotype materials fitted best onto Freundlich isotherm based on adsorption capacity values (Kf) and correlation coefficient (R2). Zeotype material Z2had the highest adsorption capacities of 4.05 and 14.01 mg/g and also removed the highest percentages of 99.89% and 99.97% for lead and cadmium ions respectively at the various conditions. Z4 indicated the lowest ability to remove lead and cadmium ions with percentages of as low as 50.00% and 57.15% respectively. However, this zeotype material demonstrated the highest ability in the removal of turbidity (46.94%) at a dosage of 0.4 g. This study demonstrates that zeotype materials can be synthesized from water hyacinth and rice husk ashes and that they can be used to effectively adsorb lead (II) and cadmium ions and coagulate turbidity from contaminated water.