LT4699B - Method for preparation of gypsum binding material - Google Patents

Abstract

The proposed invention is in the field of production of gypsum binding materials and can be used in making gypsum binding material and gypsum products out of extractive phosphate production waste - phosphogypsum. The gypsum binding material production is based on the neutralisation of semi-hydrate calcium sulphate (phosphogypsum) at high temperature (50 degrees C) in lime suspension according to the pH rise speed reaching pH 8.5-9.5.The produced pulp is neutralised, filtered, dried and ground or just poured into the forms for the further production of the articles. The rise of the pulp pH at high temperature (50 degrees C) in the interval between 11.9-11.55 and 11.0 is not higher then 0.032 units/min. and in the interval between 11.0 and 8.5-9.5 - not higher than 0.125 units/min.

Description

The present invention relates to methods for the preparation of gypsum binders and can be used to obtain gypsum binders and articles from phosphorus gypsum extraction waste.

Known method for preparing gypsum binder β-pushhydrate calcium sulfate by neutralizing phosphogypsum in a lime suspension to pH 6.5-7.5 by thickening, heat treatment and milling (see former USSR Ks 1224287, TPK C 04 B 11/00, 1986).

The disadvantage of this method is that it only processes the raw material for the production of gypsum binder, which still needs to be heat-treated in a gypsum boiler or autoclave, which requires high energy consumption.

The closest embodiment of the present invention is to provide a gypsum binder (see former USSR 391090, TPK C 04 B 11/02, 1973) from push hydrate phosphogypsum by washing it at 40-100 ° C, neutralizing it and additionally machining it. .

The disadvantages of this method are that the leaching of phosphogypsum generates a large amount of waste water, and the indicated lime neutralization when added to the phosphogypsum pulp does not allow to adjust the parameters of the neutralization process and the properties of the gypsum binder.

The object of the present invention is to obtain gypsum binder and gypsum articles using industrial phosphate fertilizer waste phosphate gypsum, which would allow to expand the raw material base and partially solve the ecological issues.

According to the present invention, the object is achieved by neutralizing the Potassium Calcium Sulphate (phosphogypsum) in a suspension of lime at high temperature (> 50 ° C) according to the pH change curve to pH 8.5-9.5, followed by filtration, drying and grinding of the the thickened pulp is poured into ready-made molds for making articles. Neutralization of phosphogypsum by adding it to a pre-prepared lime suspension with vigorous stirring and measuring (recording) pH allows to adjust the parameters of the neutralization process (to achieve a deeper degree of neutralization) and the properties of the gypsum binder.

The method of preparation is realized as follows:

Raw material.

Phosphogypsum. CaSO ₄ · 0.5 Η ₂ Ο 95 - 97%

P2O5 Pit ( _{P2O 5vt} .)

0.5-2.0% (0.3-1.5%) total (F v,.)

0.2-0.4% (0.05-0.2%)

H ₂ O bound, ie filaments at 400 ° C 5.9 - 6.0%

Lime, activity (CaO + MgO) 70 - 95%

Water to solids ratio (V / K) in pulp 1.5-3

WORKFLOW

First, it prepares a suspension of lime in hot water (filtrate), the concentration of which is soluble. The P2O5 content in the phosphogypsum is 1-15 kg / m ³ (converted to 100% (CaO + MgO). To fully hydrate the suspension, stir the suspension for 1530 min and measure and record the pH of the suspension continuously with a pH meter. lime), dosed with vigorous stirring and dispensing push hydrated phosphogypsum, which is neutralized according to the curve set up to pH 8.5-9.5. 0 is no more than 0.032 pH units / min and within the range 11.0 to 8.5-9.5 no more than 0.125 pH units / min The rate of feed of phosphogypsum depends on the amount of acid impurities present. (8.5-9.5), stops the phosphogypsum delivery, but mixes the pulp for another 10-20 minutes, then filters it and uses neutralized phosphogypsum in two ways:

- Dehydrate the hot phosphate pellet at 100-120 ° C. The dry material is then ground in a ball mill.

- Fill molds with hot push hydrated phosphogypsum to form gypsum products for various applications.

example:

With an experimental reactor capacity of 0.05 m ³ (Lifosa AB laboratory), 0.135 kg of lime (converted to 100% (CaO + MgO)) is added to a volume of 0.015 m ³ of hot (in this case 60 ° C) min The pH of the suspension is measured with a pH meter. At a constant pH of 11.55 at 60 ° C, it doses hot (in this case 60 ° C) phosphogypsum, a push hydrated calcium sulphate removed from the carousel vacuum filter for extraction of phosphoric acid (without additional washing) pH curve to pH 9.5, ie no more than 0.032 pH units / min for the pulp pH range, and no more than 0.125 for the pH range from 11.0 to 9.5 pH units / min. The hot pulp is then filtered, dried and the resulting material milled to a specific surface of PSX 350-400 m ² / kg. Properties of the resulting gypsum binder:

PH of the substance: 6.3;

Damage (times),%: 6,1;

Binding times, min: start 65; end 80;

Normal dough consistency V / G: 0.40;

Compressive strength, MPa: after 2h from end of bonding -3.6; 24 h after formation - 11.7; dry - 28.0;

Complete hydration (k = 19.9%) after 14 days.

The gypsum binder obtained in this way can be used in the manufacture of various articles, in the installation of rain floors, in the production of dry mixes, etc.

example:

Initially, for example, only phosphogypsum is neutralized to pH 8.5. It then filters the pulp to 45% moisture (can be adjusted to a well-formed dough consistency) and pours into prepared molds. As the mass hardens, the shapes disintegrate. The samples are kept in a humid environment ((> 90%) and then dried.

Properties of test specimens:

Binding times, min: start * 30; end - 50;

Compressive strength, MPa: 2 h after the end of binding, 4.1; 24 h after formation - 6.2; dry -18.0;

Complete hydration (k = 19.9%) after 24 h.

The gypsum products thus obtained can be used for various interior structures in construction.

Advantages over the prototype:

- Phosphogypsum does not need to be rinsed with hot water.

no contaminated waste water is formed;

By neutralizing the push hydrate phosphogypsum in a lime suspension at high temperature (> 50 ° C), the pH change rate curve to pH 8.5-9.5 can be used to adjust the neutralization process (to achieve a complete degree of neutralization) of phosphogypsum impurities and gypsum binder properties.

Claims (5)

DEFINITION OF INVENTION A process for the preparation of gypsum binder from push hydrate phosphogypsum by neutralizing the harmful impurities therein with further treatment of the resulting product, characterized in that the push hydrate phosphogypsum is neutralized in a lime suspension at a high temperature according to the PH rate curve. 2. A process for the preparation of a gypsum binder according to claim 1, characterized in that the neutralization of the phosphogypsum is carried out at a high temperature (> 50 ° C) to pH 8.59.5. 3. A process for the preparation of a gypsum binder according to claims 1 and 2, characterized in that the pH of the pulp changes at a high temperature (> 50 ° C) in the pH range from 11.9 to 11.55 to 11.0 up to 0.032 pH units / min. ., and in the range 11.0 to 8.5-9.5 not more than 0.125 pH units / min. 4. A process for the preparation of gypsum binder according to claims 1, 2 and 3, characterized in that the resulting neutralized slurry is filtered, dried and milled. 5. A process for the preparation of gypsum binder according to claims 1, 2 and 3, characterized in that only the thickened neutralized pulp is poured into ready-made molds.