초록 ▼

Chemical and aqueous components of sludge derived from lime treatments of raw water supplies are recovered by procedures involving carbonation of the sludges to effect a phase separation between magnesium and calcium components. When the magnesium content of the raw water is intolerable in the treat

Chemical and aqueous components of sludge derived from lime treatments of raw water supplies are recovered by procedures involving carbonation of the sludges to effect a phase separation between magnesium and calcium components. When the magnesium content of the raw water is intolerable in the treated water, a magnesium carbonate is recovered from the liquid phase by its decarbonation, and the aqueous component of the liquid phase is recycled to recover the water values of the treated sludge. When the magnesium content of the raw water can be tolerated in the treated water, the liquid phase magnesium bicarbonate solution is recycled to the water treatment plant. Turbidity factors separated with the sludges remain with the insoluble calcium carbonate that is separated from the liquid phase and by avoiding conventional coagulants other than magnesium hydroxide in the treatment of the raw water, turbidity and calcium carbonate components can be separated as by conventional froth flotation procedures to recover a quality lime product. Special procedures are used in the carbonation step when flue gases are used for sludge carbonation purposes so as to avoid contamination of recovered lime with magnesium values and special procedures are advocated in the treatment of soft turbid water supplies as well as high magnesium turbid water supplies to avoid disposal of environmental contaminating chemical flocculants such as alum.

대표청구항 ▼

The method of recovering calcium values from an aqueous sludge product of the lime treatment of raw water and which is separated from the treated water and contains an aqueous component and an intimate mixture of precipitated calcium carbonate and precipitated magnesium hydroxide, said method compri

The method of recovering calcium values from an aqueous sludge product of the lime treatment of raw water and which is separated from the treated water and contains an aqueous component and an intimate mixture of precipitated calcium carbonate and precipitated magnesium hydroxide, said method comprising the steps of: A. carbonating the separated aqueous sludge product to solubilize the precipitated magnesium hydroxide of the separated sludge product in the aqueous component of the separated sludge product, thereby to provide a carbonated sludge product which has a liquid phase component that contains the solubilized magnesium hydroxide and which has residual solids that include the precipitated calcium carbonate, B. separating the residual soliDs from the liquid phase component of the carbonated sludge product, and C. calcining the precipitated calcium carbonate of the separated residual solids obtained from the separating step (B) and recovering the calcium values of the separated aqueous sludge product as a calcined lime product; said carbonating step comprising steps of: A-1. maintaining a flow path of the separated aqueous sludge product through a plurality of serially connected sludge treatment zones by continuously introducing progressively diminishing portions of the separated aqueous sludge product to successive treatment zones along the path of the maintained flow, A-2. continuously introducing scrubbed flue gases at the bottoms of each of the respective zones, A-3. continuously and intimately mixing the flue gases introduced in the respective treatment zones with the flowing aqueous sludge therein, A-4. continuously withdrawing the introduced gases remaining from the intimate mixture thereof with the flowing aqueous sludge from the tops of each of the respective zones, and A-5. continuously withdrawing the carbonated sludge product from the last of the treatment zones along the maintained flow path; said separated aqueous sludge product being maintained between 15°C. and 21°C. during its flow through the sludge treatment zones, said carbonated sludge product being maintained between 15°C. and 21°C. during the separation step (B), said flowing aqueous sludge being maintained under substantially atmospheric pressure conditions during its flow through the treatment zones, and said portions of the separated aqueous sludge product introduced to the treatment zones having a magnesium content less than 6.5 grams per liter (as MgO).