LT4698B - Method for preparation of gypsum binding material - Google Patents

Abstract

In this invention a method of making gypsum binding material is described, when alkaline neutralising agent is added to the waste material - gypsum semi hydrate (basanite) that is formed during the phosphate extraction process. The neutralised mix is mechanically activated by rubbing till loose water is separated in the carcasses of the crystals. The produced mass is used as binding material.

Description

The invention relates to a technology for the production of inorganic materials, that is to say gypsum binders obtained from phosphogypsum (waste) obtained by extraction of phosphoric acid with sulfuric acid from apatites.

A known method for preparing gypsum β-pushahydrate from neutralizing phosphogypsum with active calcium oxide is a solid to water ratio of 1: 4 and the pH varies between (12.8-12.0) and (12.066.5) per minute (USSR) al No. 1224287).

Known waste from hydrofluoric acid production of gypsum by neutralizing acids using a ferroslag melt powder which is readily dispersed in a binder mass (RU Patent No. 2046097).

The closest possible preparation of gypsum binder is the addition of dehydrated phosphogypsum additive to phosphogypsum in a ratio (0.6-1.8): 1 and mass mixing (USSR a.l. No. 1592281).

The disadvantage of these technologies is that all gypsum binders use a lot of energy and therefore have a high cost.

The object of the present invention is to obtain high strength binders from the phosphogypsum waste obtained by extraction of phosphoric acid from apatite with sulfuric acid without the use of thermal dehydration after neutralization of the phosphogypsum.

Mechanical activation by the removal of alkaline agent-neutralized gypsum (basanite) releases the unbound water contained in the crystal skeletons. Therefore, the mechanism of formation of the hardening structure differs from the conventional hardening of solid hydrate gypsum. In the initial step of solidifying gypsum gypsum, the structure forms a gypsum skeleton in the presence of neutralizing agents in one case magnesium hydroxide, in the other case in the presence of Portland cement and SiCty micro dust. Relaxation of water from the crystal skeleton increases the binding mass density and adds strength and water resistance.

The object of the invention is achieved by the addition of a neutralizing agent, amorphous magnesium hydroxide gel, to freshly made push hydrate gypsum (basanite) in the process of extraction of phosphoric acid. The neutralized mixture is not heat treated. Its water-gypsum ratio (V / G) with magnesium hydroxide to a dough of normal consistency is controlled by the addition of water to the binder. Alternatively, the remainder of ferro-silicon from Portland cement and SiCh microparticles, a neutralization agent, is added to freshly made phosphogips (basanite). The ratio of Portland cement to SiO: micropowder in the mixture is 2: 1, and the ratio of phosphogypsum to neutralizing agent is 2.4: (0.7-1.3). The V / G of the prepared mixture is also adjusted with a water additive until the dough reaches its normal consistency.

In the first and second cases, the resulting mixtures are used as a binder for various applications, such as for the production of concrete products for environmental management, for soil stabilization in road construction, for casting of monolithic floors, etc.

The ratio of phosphogypsum to additives must be as defined in this patent, since reducing the amount of additives decreases the binding properties of the binder. As the amount of additives increases, the influence of the binder on the binding properties no longer improves, remains in the same order, and the cost price increases.

The basic raw material for the gypsum binder is fresh phosphogypsum (basanite), which is used after cooling to a temperature of at least 50 ° C. The average chemical composition of phosphogypsum is presented in Table 1.

table

The title CaO MgO Fe ₂ O ₃ A1 ₂ O ₃ F ie ₃ pH P, O ₅ overall P, O ₅ vacant H ₂ O general Phosphogips CaSO ₄ 0.5H ₂ O,% by weight 28.23 - 0.08 0.21 0.4 41.18 2.42 1.31 0.67 26.8

For testing we used:

Magnesium hydroxide gel according to TS 5666739-30-96,

Portland Element under 42.5 BS 1455.1996,

S1O2 Micro dust imported from Poland (Ferro-silicon waste). They were obtained at 3000 ° C (particle size 0.1-0.15µ).

The invention is illustrated by the following examples:

Example: 150 g of 75% moisture content of magnesium hydroxide gel is added to a sample of 3000 g of phosphogypsum (CaSChO ^ LLO), taken directly from the waste disposal line, at a temperature of> 50 ° C. Dry solids weight ratio 1: 0.0125;

Example 2: To a sample of 2400 g of phosphogypsum (CaSO ₄ -0.5H ₂ O) add 1000 g of a mixture of Portland cement and S1O2 micro dust (the dry matter ratio in the mixture is 68% Portland cement and 32% S1O2 micro dust). The ratio of phosphogypsum (CaSO ₄ -0.5H ₂ O) to additive is 2.4: 1. V / G of prepared masses is adjusted by adding water to normal dough consistency.

In both cases, the mixtures were stirred by mechanical activation at a standstill after 45 min.

The binder masses thus produced are used for molding test specimens.

Samples of both compositions are designated by numbers 1-9 and 10-18, respectively, and the compositions and properties are given in Table 2.

As can be seen from the data in Table 2, mechanical activation produced a high-quality phosphogypsum binder, from which the physical-mechanical properties of the samples produced were significantly higher than those known in the art. The resulting gypsum binder is resistant to moisture.

The proposed binders are ecologically clean, since phosphoric acid and fluorine are neutralized in the phosphogypsum with alkaline additives.

table

Fig. No. Properties of binder Mass ratio of phosphogypsum to additives: Mixing time, min Water and binders material gos, V / G The water gained the rime, % With- softening coeff. K Strength after 28 h Magnesium hydroxide gel Mixture of cement and SiO, a micro-dust Compressive (R ^) MPa Bending (Ri) MPa 1 1: 0.0125 - 45 0.22 5.9 0.92 22.5 9.6 2 1: 0.005 - 45 0.21 7.7 0.82 15.6 7.4 3 1: 0.020 - 45 0.22 5.9 0.91 21.1 8.7 4 1: 0.0125 - 30th 0.22 8.2 0.80 18.8 8.9 5 1: 0.0125 - 60 0.22 6.1 0.88 21.9 9.2 6th 1: 0.0045 - 45 0.21 8.0 0.79 14.0 6.3 7th 1: 0.025 - 45 0.22 5.8 0.90 21.7 9.0 8th 1: 0.0125 - 20th 0.22 8.4 0.78 13.4 5.1 9th 1: 0.0125 - 70 0.22 - 6.0 0.88 22.3 9.4 10th - 2.4: 1 45 0.36 2.1 0.87 42.9 14.3 11th - 2.4: 0.7 45 0.32 2.4 0.78 30.2 10.1 12th - 2.4: 1.3 45 0.39 2.3 0.83 39.9 13.0 13th - 2.4: 1 30th 0.36 3.0 0.75 27.7 12.6 14th - 2.4: 1 60 0.36 2.1 0.85 42.0 13.9 15th - 2.4: 0.6 45 0.32 2.6 0.75 29.1 9.3 16th - 2.4: 1.4 45. · 0.40 2.3 0.86 41.7 14.0 17th - 2.4: 1 20th 0.36 3.2 0.71 25.3 10.8 18th - 2.4: 1 70 0.36 2.2 0.87 42.3 14.0 19th know- mas 1: 0.9 * - 10th - - 6.1 3.3

- Dehydrated phosphogypsum

Claims (3)

Definition of the Invention CLAIMS 1. A method of preparing a gypsum binder comprising neutralizing and mixing phosphogypsum, characterized in that phosphogyps is neutralized with magnesium hydroxide gel in a ratio of 1: (0.005-0.02) by activating the components in a mechanical blender for 30-60 min. 2. Method according to claim 1, characterized in that the Portland cement and phosphogypsum neutralize sich microsilica mixture _f ratio 2.4 (0.7 to 1.3). 3. Gypsum binder, characterized in that it is obtained according to claim 1 or 2.