Method for producing phosphoric acid and calcium sulphate quality suitable for a clinker process for the commercial and industrial utilization of calcium sulphate

Patent metadata

Field	Value
Publication number	US-2023373789-A1
Application number	US-202117791687-A
Country	US
Kind code	A1
Filing date	Jan 5, 2021
Priority date	Jan 8, 2020
Publication date	Nov 23, 2023
Grant date	—

Abstract

A process may involve digesting raw phosphate with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in the form of dihydrate and/or hemihydrate, and phosphoric acid, separating off calcium sulfate as solid from a liquid phase of a suspension that is obtained, treating the calcium sulfate that is separated off or from a stockpile with an acid to give a suspension with purified calcium sulfate and P 2 O 5 -containing acid solution, separating off the purified calcium sulfate as solid from a liquid phase of a suspension obtained, using the P 2 O 5 -containing liquid phase as a portion of the sulfuric acid required for digesting the raw phosphate or as feedstock for treating phosphogypsum from the stockpile to give a suspension of purified calcium sulfate and P 2 O 5 -containing acid solution, which is thereafter processed.

First claim

1 .- 28 . (canceled)

29 . A process for producing phosphoric acid and purified calcium sulfate by reaction of raw phosphate with sulfuric acid, the process comprising:
a) digesting the raw phosphate in a first step with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in a form of dihydrate, hemihydrate, or a combination of hemihydrate and dihydrate, and phosphoric acid; b) separating off the calcium sulfate as a solid from a liquid phase of a suspension that is obtained; c) treating the calcium sulfate from step (b), separated off from the phosphoric acid, and/or calcium sulfate/phosphogypsum from a stockpile with an acid to give a suspension with purified calcium sulfate and a P 2 O 5 -containing acid solution; d) separating off the purified calcium sulfate after step (c) as a solid from a liquid phase of the suspension that is obtained, wherein the separation of the purified calcium sulfate from the suspension is started at a time in a range from t MIN +30 minutes to t MIN −30 minutes, wherein t MIN is a time at which an acid concentration during the treatment in step (c) is a minimum; and e) at least one of
e1) using a P 2 O 5 -containing liquid phase obtained from step (d) as feedstock in step (a) as a portion of the sulfuric acid required for digesting the raw phosphate, or
e2) using a P 2 O 5 -containing liquid phase obtained from step (d) as feedstock for treating phosphogypsum from the stockpile in step (c) to give a suspension of purified calcium sulfate and an P 2 O 5 -containing acid solution.

30 . The process of claim 29 wherein the separation of the purified calcium sulfate from the suspension in step (d) is started at a time in a range from t 1 +20 minutes to t 1 −20 minutes, wherein t 1 is a time at which the acid concentration during the treatment in step (c) has been reduced by at least 1.0% of an initial acid concentration.

31 . The process of claim 29 wherein the separation of the purified calcium sulfate from the suspension in step (d) is started at a time in a range from t MIN +15 minutes to t MIN −15 minutes.

32 . The process of claim 29 wherein the treatment of the calcium sulfate/phosphogypsum from the stockpile without the calcium sulfate from step (b) is treated in a separate step with an acid and either
a suspension that is formed is supplied to step (d), or
a suspension that is formed is supplied to a separate separating unit and in the separate separating unit a solid is separated from a liquid phase comprising a P 2 O 5 -containing acid solution.

33 . The process of claim 29 wherein the calcium sulfate is separated off from the phosphoric acid in step (b) by filtration.

34 . A process for producing sulfuric acid and cement clinker, the process comprising:
a) digesting raw phosphate in a first step with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in a form of dihydrate, hemihydrate, or a combination of hemihydrate and dihydrate, and phosphoric acid; b) separating off the calcium sulfate as a solid from a liquid phase of a suspension that is obtained; c) treating the calcium sulfate from step (b), separated off from the phosphoric acid, and/or calcium sulfate/phosphogypsum from a stockpile with an acid to give a suspension with purified calcium sulfate and a P 2 O 5 -containing acid solution; d) separating off the purified calcium sulfate after step (c) as a solid from a liquid phase of the suspension that is obtained, wherein the separation of the purified calcium sulfate from the suspension is started at a time in a range from t MIN =30 minutes to t MIN −30 minutes, wherein t MIN is a time at which an acid concentration during the treatment in step (c) is a minimum; and e) mixing the purified calcium sulfate that is separated off and obtained in step (d) with admixtures and reducing agent to give a raw meal mixture for cement clinker production; f) burning the raw meal mixture to give the cement clinker, with sulfur dioxide being formed as an offgas; and g) supplying the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.

35 . The process of claim 34 wherein the separation of the purified calcium sulfate from the suspension in step (d) is started at a time in a range from t 1 +20 minutes to t 1 −20 minutes, wherein t 1 is a time at which the acid concentration during the treatment in step (c) has been reduced by at least 1.0% of an initial acid concentration.

36 . The process of claim 34 wherein the separation of the purified calcium sulfate from the suspension in step (d) is started at a time in a range from t MIN +15 minutes to t MIN −15 minutes.

37 . The process of claim 34 wherein the treatment of the calcium sulfate/phosphogypsum from the stockpile without the calcium sulfate from step (b) is treated in a separate step with an acid and either
a suspension that is formed is supplied to step (d), or
a suspension that is formed is supplied to a separate separating unit and in the separate separating unit a solid is separated from a liquid phase comprising a P 2 O 5 -containing acid solution.

38 . The process of claim 34 wherein the calcium sulfate is separated off from the phosphoric acid in step (b) by filtration.

39 . The process of claim 34 wherein the calcium sulfate in step (c) is either:
from the stockpile, or
obtained from a separating unit of step (b), wherein calcium sulfate filtercake obtained after a first separation from the phosphoric acid is used directly or after one or more washes with liquid.

40 . The process of claim 34 wherein at least one of:
in step (c) the acid is added in an amount such that a weight ratio of solids to liquid in the suspension is in a range from 1/5 to 1/1;
an acid resulting from the treatment in step (c) is a 3 to 10 molar acid;
the acid in step (c) is hydrochloric acid, nitric acid, sulfurous acid, and/or sulfuric acid;
the treatment in step (c) is performed at a temperature in a range from 30 to 80° C.; or
a duration of the treatment in step (c) is in a range from 15 to 90 minutes.

41 . The process of claim 34 wherein a D v (50) of a grain size distribution of calcium sulfate anhydrite obtained in step (d) is in a range of 0.5-100 μm.

42 . The process of claim 34 wherein the purified calcium sulfate from step (d) accounts for more than 70% by weight of a total calcium sulfate in the raw meal mixture.

43 . A plant for producing phosphoric acid and purified calcium sulfate by reaction of raw phosphate with sulfuric acid, the plant comprising:
a) a reaction unit that includes (i) a raw phosphate feed and (ii) a concentrated sulfuric acid feed line, wherein the reaction unit is configured to form a suspension comprising phosphoric acid and calcium sulfate, with the calcium sulfate being present in the form of dihydrate, hemihydrate, or a combination of hemihydrate and dihydrate, wherein the reaction unit includes (iii) an outlet for the suspension; b) a first separating unit configured to separate the suspension as a solid from a liquid phase, the first separating unit comprising an outlet for a substantially solid-containing phase and an outlet for a substantially liquid-containing phase, wherein the first separating unit is fluidically connected to the reaction unit; c) a purifying unit that is fluidically connected to the first separating unit and includes a feed for an acid, wherein the purifying unit is configured to convert the calcium sulfate separated off in the first separating unit and/or calcium sulfate/phosphogypsum from a stockpile into a suspension

Assignees

• Thyssenkrupp Ind Solutions Ag
• Thyssenkrupp Ag

Inventors

• Stockhoff Peter
• Helmle Stefan
• Rivas Villarreal Deyvi Javier
• Daheim Nicolai

Classifications

• C01B25/232 Primary

  Preparation by reacting phosphate containing material with concentrated sulfuric acid and subsequently lixiviating the obtained mass, e.g. clinker process · CPC title

• C01B25/234

  Purification; Stabilisation; Concentration (purification concomitant with preparation C01B25/22; preparation involving solvent-solvent extraction C01B25/46) · CPC title

• C04B11/005

  Preparing or treating the raw materials · CPC title

• C01F11/468

  Purification of calcium sulfates · CPC title

• C01B17/74 Primary

  Preparation · CPC title