Method of manufacturing high purity calcium carbonate

A method of producing high purity calcium carbonate from lime kiln dust exhausted from a lime kiln, the method consisting essentially of:

• mixing lime kiln dust containing calcium oxide with water so that an aqueous suspension is formed, and wherein calcium oxide in the lime kiln dust is hydrated to form calcium hydroxide;
• allowing solids within the suspension to settle so that a clear, saturated solution of calcium hydroxide is formed;
• contacting the clear, saturated solution of calcium hydroxide with carbon dioxide gas so that the calcium hydroxide reacts with the carbon dioxide to form a high purity calcium carbonate precipitate;
• allowing the high purity calcium carbonate precipitate to settle from supernatant water of the solution;
• separating the high purity calcium carbonate from the supernatant water;
• and
• wherein the supernatant water is recycled and used as the water mixed with the lime kiln dust to form the suspension.

A method of treating flue gases containing lime kiln dust exhausted from a lime kiln wherein one of the byproducts of such treatment is high purity calcium carbonate, the method consisting essentially of:

• passing flue gases exhausted from the lime kiln through a kiln dust separator so that lime kiln dust containing calcium oxide is removed;
• mixing the removed lime kiln dust with water so that an aqueous suspension of the lime kiln dust is formed, and wherein the calcium oxide in the lime kiln dust is hydrated to form calcium hydroxide;
• allowing solids within the suspension to settle so that a clear, saturated solution of calcium hydroxide is formed;
• contacting the clear, saturated solution of calcium hydroxide with carbon dioxide gas so that the calcium hydroxide reacts with the carbon dioxide to form a high purity calcium carbonate precipitate;
• allowing the high purity calcium carbonate precipitate to settle from supernatant water of the solution;
• separating the high purity calcium carbonate precipitate from the supernatant water;
• and
• wherein the supernatant water is recycled and used for mixing with the lime kiln dust to form the suspension.

A method of treating flue gases containing lime kiln dust exhausted from a lime kiln to produce high purity calcium carbonate having a generally cuboidal-shaped crystalline structure, the method comprising:

• passing flue gases exhausted from the lime kiln through a kiln dust separator so that lime kiln dust containing calcium oxide is removed from the flue gas;
• mixing the lime kiln dust with water so that an aqueous suspension of the lime kiln dust is formed, and wherein the calcium oxide in the lime kiln dust is hydrated to form calcium hydroxide;
• allowing solids within the suspension to settle so that a clear, saturated solution of calcium hydroxide having a pH of about 12.4 is formed;
• contacting the clear, saturated solution of calcium hydroxide with carbon dioxide gas so that the calcium hydroxide reacts with the carbon dioxide to form a high purity calcium carbonate precipitate in the form of particles having a generally cuboidal-shaped crystalline structure;
• allowing the high purity calcium carbonate precipitate to settle from supernatant water of the solution;
• then
• separating the high purity calcium carbonate precipitate from the supernatant water;
• and then
• recycling the supernatant water as the water mixed with the lime kiln dust to form the aqueous suspension.