Abrégé

2) and having a pH of at least 11.5; (ii) treating the solution prepared in step (i) to remove solids including suspended solids; (iii) dispersing carbon dioxide through the solution so as to form calcium carbonate with a consequential reduction in the pH of the reaction mixture, (iv) during a time period beginning at the start of a sudden, short rise in pH and ended during a subsequent fall in pH but before it reaches 9.5 terminating the dispersion of carbon dioxide and adding an alkaline reagent to maintain a pH for the product mixture of at least 9.5, and (v) recovering precipitated calcium carbonate.

Classes IPC  ?

• C01F 11/18 - Carbonates
• C01F 11/02 - Oxydes ou hydroxydes
• B01D 53/62 - Oxydes de carbone
• C07C 31/18 - Alcools polyhydroxyliques acycliques

Abrégé

A method of producing calcium carbonate from a waste sludge containing calcium carbonate and at least one silicate mineral. The method comprises the steps of: (i) incinerating the sludge to an ash in which at least 60 % of the calcium carbonate present in the sludge is converted to free calcium oxide which is unreacted with the silicate mineral(s), (ii) optionally slaking the ash to convert at least a portion of the free calcium oxide therein to calcium hydroxide, (iii) treating either the ash from step (i) or the slaked ash from step (ii) with an aqueous solution of a polyhydroxy compound to provide a solution of dissolved calcium hydroxide, (iv) separating insoluble material from the solution of calcium ions obtained in step (iii), (v) dispersing carbon dioxide through the solution obtained from step (iv) so as to produce calcium carbonate, and (vi) separating the calcium carbonate produced in step (v). The silicate mineral may be kaolin. The invention allows the production of metakaolin substantially devoid of free lime as an additional product stream.

Classes IPC  ?

• C01F 11/02 - Oxydes ou hydroxydes
• C01F 11/06 - Oxydes ou hydroxydes par décomposition thermique de carbonates
• C01F 11/18 - Carbonates
• F23G 5/00 - Procédés ou appareils, p. ex. incinérateurs, spécialement adaptés à la combustion de déchets ou de combustibles pauvres

Abrégé

A method of producing calcium carbonate from lime comprises the steps of: (i) providing an aqueous solution comprising 10% to 35% by weight of dissolved polyhydroxy compound and 1% to 5% by weight of dissolved calcium hydroxide (expressed as Ca(OH)2) and having a pH of at least 11.5; (ii) treating the solution prepared in step (i) to remove solids including suspended solids; (iii) dispersing carbon dioxide through the solution so as to form calcium carbonate with a consequential reduction in the pH of the reaction mixture, (iv) during a time period beginning at the start of a sudden, short rise in pH and ended during a subsequent fall in pH but before it reaches 9.5 terminating the dispersion of carbon dioxide and adding an alkaline reagent to maintain a pH for the product mixture of at least 9.5, and (v) recovering precipitated calcium carbonate.

Classes IPC  ?

• C01F 11/00 - Composés du calcium, du strontium ou du baryum
• C01F 11/18 - Carbonates

Abrégé

A method of producing calcium carbonate from lime comprises the steps of: (i) providing an aqueous solution comprising 10% to 35% by weight of dissolved polyhydroxy compound and 1% to 5% by weight of dissolved calcium hydroxide (expressed as Ca(OH)2) and having a pH of at least 11.5; (ii) treating the solution prepared in step (i) to remove solids including suspended solids; (iii) dispersing carbon dioxide through the solution so as to form calcium carbonate with a consequential reduction in the pH of the reaction mixture, (iv) during a time period beginning at the start of a sudden, short rise in pH and ended during a subsequent fall in pH but before it reaches 9.5 terminating the dispersion of carbon dioxide and adding an alkaline reagent to maintain a pH for the product mixture of at least 9.5, and (v) recovering precipitated calcium carbonate.

Classes IPC  ?

• C01F 11/00 - Composés du calcium, du strontium ou du baryum
• C01F 11/18 - Carbonates