Method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in phosphoric acid dihydrate-hemihydrate wet extraction process

A technology of calcium sulfate dihydrate and calcium sulfate hemihydrate, applied in chemical instruments and methods, phosphorus compounds, calcium/strontium/barium compounds, etc., can solve problems such as low additional utilization value, reduced separation rate, waste of sulfur resources, etc. Achieve the effect of uniform crystal growth size and shape, uniform shape and size

Pending Publication Date: 2021-09-28
EAST CHINA ENG SCI & TECH
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The main drawbacks of flaky dihydrate phosphogypsum in the wet process phosphoric acid process are that when the solid-liquid phase is separated, the calcium sulfate crystals in the solid are prone to layer-by-layer stacking, and the separation rate is reduced during the filtration and washing process, and the residual phosphorus in the gypsum The content is high, and compared with calcium sulfate hemihydrate, calcium sulfate dihydrate, which is the main component of phosphogypsum dihydrate, has low additional utilization value and is a solid waste in industrial production.
Dihydrate process and dihydrate phosphogypsum not only bring loss of phosphorus resources, but also waste of sulfur resources and pollution
[0009] To sum up, in the existing wet-process phosphoric acid industry, it is difficult to produce hemihydrate gypsum with uniform shape, size and particle size distribution through phosphoric acid leaching at low temperature (about 100°C). The salt solution method (the mass ratio of salt solution to gypsum far exceeds 1:1) cannot be realized in the wet process phosphoric acid industry

Method used

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  • Method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in phosphoric acid dihydrate-hemihydrate wet extraction process
  • Method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in phosphoric acid dihydrate-hemihydrate wet extraction process
  • Method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in phosphoric acid dihydrate-hemihydrate wet extraction process

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Effect test

Embodiment 1

[0045] The invention provides a kind of method that calcium sulfate dihydrate converts calcium sulfate hemihydrate into α-calcium sulfate hemihydrate in the process of dihydrate-semiwater wet leaching phosphoric acid, such as Figure 1-6 As shown, the embodiment of the present invention uses the phosphate rock of a phosphate rock in a certain area of ​​Hubei as raw material, and the composition Wt (%) of the phosphate rock is as follows:

[0046] Element P 2 o 5

MgO CaO Al 2 o 3

Fe 2 o 3

K 2 o

N 2 o

SiO 2

F other content / % 31.18 1.07 45.51 2.88 3.16 3.20 1.63 2.64 2.73

[0047] The first stage: at low temperature (≤85°C), phosphate ore is extracted by sulfuric acid, phosphoric acid is extracted, and CaSO is produced by reaction at the same time 4 2H 2 O (calcium sulfate dihydrate).

[0048] The second stage: raise the temperature to above 100°C, and the reaction process is in the crystal transform...

Embodiment 2

[0056] Using the same phosphate rock as in Example 1 as the raw material, the reaction conditions in the first stage are the same, but the compound additive is added in three steps in the second stage. %; add 10-25% of the total amount of compound additives in the stable transformation stage of 8-120min; add 5-25% of the total amount of compound additives in the crystal growth stage of 120-150min.

[0057] The conversion agent, buffering agent and phase transfer agent in the composite additive are mixed components, wherein the conversion agent is sodium sulfate accounting for 40% of the total composite additive; the buffering agent is succinic acid accounting for 2.5% of the total composite addition and The total amount of 2.5% oxalic acid; the phase transfer agent selects polyethylene glycol accounting for 2.5% of the total amount of compound addition and polyvinyl alcohol accounting for 2.5% of the total amount of compound addition; the auxiliary agent is water; the mass of t...

Embodiment 3

[0061] Using the same phosphate rock as in Example 1 as the raw material, the reaction conditions in the first stage are the same, but the compound additive is added in three steps in the second stage. %; add 10-25% of the total amount of compound additives in the stable transformation stage of 8-120min; add 5-25% of the total amount of compound additives in the crystal growth stage of 120-150min.

[0062] The conversion agent, buffering agent and phase transfer agent in the composite additive are mixed components, wherein the conversion agent is potassium sulfate accounting for 40% of the total composite additive; the buffering agent is succinic acid and 2.5% of the total composite additive The total amount of 2.5% oxalic acid; the phase transfer agent selects polyethylene glycol accounting for 2.5% of the total amount of compound addition and polyvinyl alcohol accounting for 2.5% of the total amount of compound addition; the auxiliary agent is water; the mass of the compound ...

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Abstract

The invention discloses a method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in a phosphoric acid dihydrate-hemihydrate wet extraction process, which comprises the following steps of: 1, extracting phosphorite by sulfuric acid at low temperature, extracting phosphoric acid, and reacting to produce CaSO4. 2H2O; 2, increasing the temperature to 100 DEG C or above, the reaction process is in a crystal transformation stage, and on the premise that phosphoric acid is not separated and leached, generated CaSO4. 2H2O is converted into alpha-CaSO4. 5H2O with controllable morphology and length-diameter ratio by additionally adding a composite crystal transformation agent. According to the method disclosed by the invention, by utilizing the composite additive which mainly comprises the inorganic sulfate transforming agent, the organic acid, the organic acid salt buffering agent, the water-soluble dispersing agent and the auxiliary agent, flaky CaSO4. 2H2O is promoted to be transformed into columnar alpha-CaSO4. 5H2O on the premise of not separating phosphoric acid slurry in a one-step wet-process phosphoric acid production process. In the phosphoric acid production process, the direct high-added-value utilization of the dihydrate gypsum solid waste is realized.

Description

technical field [0001] The invention belongs to the technical field of wet-process phosphoric acid production, and in particular relates to a method for converting calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate in a process of dihydrate-semihydrate wet leaching phosphoric acid. Background technique [0002] The production process of wet-process phosphoric acid is distinguished by the type of phosphogypsum produced. The main components of phosphogypsum dihydrate, phosphogypsum hemihydrate and anhydrous phosphogypsum are CaSO 4 2H 2 O, α-CaSO 4 0.5H 2 O and CaSO 4 . The existing mature industrialized wet-process phosphoric acid processes include: dihydrate method, dihydrate-semi-water method and semi-water method. Among them, the semi-water-dihydrate method can be divided into semi-water-dihydrate dilute acid method (one-step method) and semi-water-dihydrate concentrated acid method (two-step method). The dihydrate-semi-water method currently only has tw...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C01B25/231C01F11/46
CPCC01B25/231C01F11/466C01P2006/80C01P2004/61C01P2004/60C01P2004/10
Inventor 孙祥斌钱俊刘征
Owner EAST CHINA ENG SCI & TECH
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