초록 ▼

Extraction of calcium salts from papermaking sludge or sludge-derived ash is accomplished by mixing with a solution of an inorganic or organic acid. The acid extraction typically results in solubilization of other salts as well, e.g., those of aluminum, magnesium and iron. However, because these non

Extraction of calcium salts from papermaking sludge or sludge-derived ash is accomplished by mixing with a solution of an inorganic or organic acid. The acid extraction typically results in solubilization of other salts as well, e.g., those of aluminum, magnesium and iron. However, because these non-calcium salts precipitate as hydroxides at lower pH than calcium hydroxide, a caustic (or any other alkaline agent, in a solid or liquid form) is gradually added to precipitate non-calcium salts to facilitate their removal from solution (generally by filtration or centrifugation) prior to precipitation of calcium hydroxide. The desired calcium salt is then precipitated through addition of the appropriate acid anion (either by way of the acid or a salt having greater water solubility than the resulting calcium salt).

대표청구항 ▼

[ What is claimed is:] [1.] A method of extracting calcium from an aqueous mixture comprising papermaking sludge, the mixture comprising solid and liquid phases, the method comprising the steps of:a. combining the mixture with an acid to solubilize substantially all calcium present in the mixture;b.

[ What is claimed is:] [1.] A method of extracting calcium from an aqueous mixture comprising papermaking sludge, the mixture comprising solid and liquid phases, the method comprising the steps of:a. combining the mixture with an acid to solubilize substantially all calcium present in the mixture;b. incubating the mixture;c. separating a liquid fraction, the liquid fraction comprising dissolved non-calcium salts and substantially all calcium salts, and having a pH;d. precipitating non-calcium salts, but not the calcium salts, from the liquid fraction by raising the pH thereof; ande. removing the precipitate and recovering calcium salt from the liquid fraction by subsequent precipitation.