Jul 29, 2003

Arsenic Overview Series - Part 7

Glossary of Terms

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Adsorption: A physical separation process occurring when liquids, gases, colloids, and suspended matter adhere to the surfaces of or internal pores of an adsorbent medium. It differs from absorption.

Arsenosis: An affliction caused to humans by the accumulation of arsenic in the body.

Coagulation: The process of destabilization by charge neutralization of colloidal suspended matter. Such neutralized particles, no longer repelling each other, then can be brought together and agglomerated into larger particles. A coagulant compound such as alum can be fed to neutralize the electrical surface charge on suspended solids leading to agglomeration. Also referred to as Flocculation.

Cold Lime-softening: The process wherein lime is added to cold water, usually along with a small amount of coagulant and the reaction causes bicarbonate alkalinity to precipitate as calcium carbonate. Process used mainly in municipal systems for partial hardness reduction. See also Cold Lime-Soda Softening.

Cold Lime-soda Softening: The process of adding lime and soda ash to cold water in large municipal type treatment plants, to reduce the bicarbonate and nonbicarbonate alkalinity. Usually small amounts of coagulant are used to enhance the precipitation settling step.

Ion Exchange: The process whereby ions in solution are interchanged by an insoluble reactive material. A reversible process in which ions are released from an insoluble permanent product, in exchange for other ions in a surrounding solution. The direction of the exchange depends upon the affinities of the ion exchanger resin for the ions present and the concentrations of the ions in the solution.

Reverse Osmosis: A process for the reduction of dissolved ions from water in which pressure is employed to force liquid (water) through a semi-permeable membrane, which will transmit the water but reject most other dissolved materials. When forced against the membrane surface, the dissolved materials are repelled, while the water molecules in the membrane diffuse through it molecule by molecule informing purer water on the other side.

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