Production of citrate soluble phosphates by calcination of secondary phosphate sources with a sodium-sulfuric compound

1. A method of calcination, comprising:

providing a raw material comprising whitlockite Ca 9 (Mg,Fe 2+ )[PO 3 (OH)|(PO 4 ) 6 ], and/or iron phosphate FePO 4 , and/or aluminium phosphate AlPO 4 and/or fluorapatite Ca 5 (PO 4 ) 3 F;

providing an alkaline-sulfuric compound as an additive;

providing a carbonaceous reducing agent as a second additive;

calcining a mixture of the raw material with the additives comprising reductive activation of the alkaline-sulfuric compound; and

obtaining a product, wherein the product comprises a citrate soluble phosphate compound,

wherein the carbonaceous reducing agent comprises a phosphorus containing material, selected from a sewage sludge or a biomass.

2. The method according to claim 1 , wherein the citrate soluble phosphate compound comprises CaNaPO 4 .

3. The method according to claim 1 , wherein the calcining proceeds under reducing conditions at a temperature of 800-1100° C.

4. The method according to claim 1 , wherein CaNaPO 4 is a main phosphate phase.

5. The method according to claim 1 , wherein the alkaline-sulfuric compound is selected from a sodium-sulfuric compound or a potassium sulphuric compound.

6. The method according to claim 1 , wherein the raw material contains a silicon, and an amount of the alkaline-sulfuric compound is correlated to a content of a phosphorus in the raw material and a content of the silicon.

7. The method according to claim 1 , wherein providing the alkaline-sulfuric compound is adapted to obtain in the mixture a molar ratio of Na:P of 1.1-1.8, and a molar ratio of Na:Si of 0.2-0.8, corresponding to an amount of 10 to 40 wt. % of the mixture.

8. The method according to claim 5 , wherein a first alkaline-sulfuric compound is at least partly substituted by a second alkaline-sulfuric compound comprising another alkali metal, and/or by an alkali metal carbonate, and/or by an alkali metal hydroxide.

9. The method according to claim 1 , wherein the calcining proceeds under reducing conditions at a temperature of 850-1000° C.

10. The method according to claim 1 , wherein a fraction of the carbonaceous reducing agent comprises a phosphorus containing material and is a dominant mass fraction.

11. The method according to claim 1 , wherein a sewage sludge ash contained in the raw material is completely substituted by a carbonaceous reducing agent comprising phosphorus containing material.

12. A method of calcination, comprising:

providing a raw material comprising whitlockite Ca 9 (Mg,Fe 2+ )[PO 3 (OH)|(PO 4 ) 6 ], iron phosphate FePO 4 , aluminium phosphate AlPO 4 , or fluorapatite Ca 5 (PO 4 ) 3 F;

providing an alkaline-sulfuric compound as an additive;

providing a carbonaceous reducing agent as a second additive;

calcining a mixture of the raw material with the additives comprising reductive activation of the alkaline sulfuric compound;

obtaining a product, wherein the product comprises a citrate soluble phosphate compound; and

controlling an atmosphere with respect to an oxygen concentration during calcining or during a cooling, wherein a content of sulfur in the product substantially corresponds to the content of sulfur in the mixture,

wherein the raw material is an ash selected from a sewage sludge ash or a biomass ash.

13. The method according to claim 12 , wherein the content of sulfur is water soluble, at least partly, by mildly oxidizing the product by contact to an oxidizing atmosphere or air at a reduced temperature of 300-700° C.

14. The method according to claim 12 , wherein calcining is carried out at a temperature of 800-1100° C. to obtain a stable operation condition by avoiding a baking of the product.

15. The method according to claim 12 , further comprising:

removing a heavy metal, comprising Pb, Cd, and Hg contained in the raw material by vaporization and sublimation of the reduced heavy metal species.

16. The method according to claim 15 , wherein reduction of a heavy metal is achieved by adding 10-20% of a phosphorus containing carbonaceous reducing agent and removing 30-50% of Pb, Cd, and Hg.

17. The method according to claim 15 , wherein reduction of a heavy metal is achieved by adding 25-75% of a phosphorus containing carbonaceous reducing agent and removing 40-70% of Pb, Cd, and Hg.

18. A method of calcination, comprising:

providing a raw material comprising whitlockite Ca 9 (Mg,Fe 2+ )[PO 3 (OH)|(PO 4 ) 6 ], iron phosphate FePO 4 , aluminium phosphate AlPO 4 , or fluorapatite Ca 5 (PO 4 ) 3 F;

providing an alkaline-sulfuric compound as an additive;

providing a carbonaceous reducing agent as a second additive;

calcining a mixture of the raw material with the additives comprising reductive activation of the alkaline sulfuric compound; and

obtaining a product, wherein the product comprises a citrate soluble phosphate compound,

wherein the alkaline-sulfuric compound is selected from a by-product of an industrial process selected from a rayon fiber production, a pulp manufacture, ora paper manufacture,

or the alkaline-sulfuric compound is selected from biomass, sludge, refuse derived fuel or waste incineration.

19. A process for obtaining a citrate soluble phosphate compound from a P-containing raw material, the raw material comprising a P-phase selected from whitlockite Ca 9 (Mg,Fe 2+ )[PO 3 (OH)|(PO 4 ) 6 ], iron phosphate FePO 4 , aluminium phosphate AlPO 4 or fluorapatite Ca 5 (PO 4 ) 3 F, the process comprising:

determining in the raw material a molar ratio of Na/Si and a molar ratio of Na/P;

determining a quantity of a sodium-sulfuric compound based on the determined molar ratio of Na/Si and Na/P;

calcining under reducing conditions the raw material together with the determined quantity of the sodium-sulfuric compound to obtain the citrate soluble phosphate compound;

wherein the step of determining the quantity of the sodium sulfuric compound comprises:

detecting a sodium quantity required to obtain by calcining the raw material the citrate soluble phosphate compound CaNaPO 4 by conversion of the P-phase; and

calculating an amount of the sodium-sulfuric compound corresponding to the detected sodium quantity, wherein the sodium-sulfuric compound is selected from Na 2 S, Na 2 SO 3 , or Na 2 SO 4 .

20. The process according to claim 19 , wherein the sodium quantity is detected according to the following formula

n Me =x·n P +y·n Si ,

wherein n Me is the amount of sodium expressed in moles, n P is the amount of phosphorus in the raw material expressed in moles, n Si is the amount of silica in the raw material expressed in moles, whereas x and y are coefficients expressing the consumption of alkali metal in alkali metal consuming reactions during calcining.

21. The process according to claim 20 wherein x is selected from the range of 0.8-1.8; and y is selected from the range of 0.25-0.6,

and wherein the citrate solubility is detected with aqueous ammonium citrate and comprises 35-100% of a total P content.

22. The process according to claim 19 , further comprising:

controlling an atmosphere with respect to an oxygen concentration during calcining or during a cooling.

23. The process according to claim 22 , wherein the step of controlling is adapted to prevent accumulation of a pyrite type iron-sulfur-compound Fe 7 S 8 ; to prevent complete combustion of the pyrite type iron-sulfur compound Fe 7 S 8 and/or to obtain a water soluble sulfuric compound with sodium sulfate as a main phase.