Patent ID: 6863819
Filing Date: 2005-03-08
Classification: C02F,Y10S

Abstract:
1. A method of treating acid raw water containing sulphate anions, the method including the steps of neutralising the raw water by adding calcium carbonate to the raw water in a neutralising stage, rendering the neutralised water alkaline or more alkaline by adding thereto an alkali selected from the group consisting of calcium hydroxide, calcium oxide and mixtures thereof in a lime treatment stage, and then treating alkaline water from the lime treatment stage with carbon dioxide in a carbon dioxide treatment stage, the carbon dioxide reacting, in the carbon dioxide treatment stage, with calcium hydroxide dissolved in the water to precipitate calcium carbonate, the treating of the alkaline water with carbon dioxide including feeding carbon dioxide produced in the neutralising stage according to the reaction: into the alkaline water from the lime treatment stage, to react with calcium hydroxide in the water at a pH of not less than 8.3 according to the reaction: calcium carbonate produced as a precipitate in the carbon dioxide treatment stage forming at least part of the calcium carbonate added to the raw water in the neutralising stage, the alkali addition in the lime treatment stage acting to precipitate one or more calcium sulphate-containing compounds, the process including separation of calcium sulphate-containing precipitate from the water issuing from the lime treatment stage before it is treated with carbon dioxide in the carbon dioxide treatment stage, and the carbon dioxide fed into the carbon dioxide treatment stage acting to render the water issuing from the carbon dioxide treatment stage undersaturated with regard to calcium sulphate.