Alumina - silicon series refractory bentonite

Bentonite is abundant and widely distributed in the world, with a total reserve of about 2.5 billion t. The United States, the former Soviet Union and China account for three-quarters of the world's reserves, followed by Italy, Greece, Australia and Germany. Calcium bentonite accounts for about 70%~80%, and sodium bentonite reserves less than 500 million t. Therefore, although bentonite resources are very rich, but the largest amount of high quality sodium bentonite is very short. The bentonite in China is 90% calcium bentonite. Bentonite ore deposits cover 23 provinces in China, and there are more than 20 large deposits.

The application of bentonite in refractory materials is mainly to use its excellent plasticity to improve the plasticity, suspension, viscosity or adhesion of refractory mud, refractory coating or spraying coating. Due to its large amount of water absorption, in order to avoid larger shrinkage, ensure high temperature performance, generally add less.

Bentonite, also known as porphyrodeite and Bentonite, is a clayey rock with montmorillonite as its main component (up to 85%~90%). It is also a relatively soft rock that is metamorphosed by natural volcanic ash in geological time. According to the type, content and layer charge of montmorillonite exchangeable cations, bentonite can be divided into three types: sodium bentonite, calcium bentonite and bleached soil. Among them, calcium bentonite includes calcium sodium base, calcium magnesium base bentonite.

The main mineral of bentonite is Montmoril-lonite, a water-bearing aluminosilicate mineral containing a small amount of alkali or alkaline earth metals. It belongs to the aluminosilicate group and has strong water absorption, cation exchange ability, expansibility, plasticity and binding ability. Montmorillonite is Al ₂ O ₃ aqueous silicate as the main body of the clay minerals content, complicated composition. Its chemical general formula is: Na ₓ (H ₂ O ₄) {(Al ₂ ₓ MgO style ₓ) [Si ₄ ₁ O zero] (OH) ₂ or shorthand for mAl ₂ O ₃ - nSiO ₂ - XH ₂ O, or further abbreviated to Al ₂ O ₃ · 4 the sio ₂ · nH ₂ O.

Bentonite often contains a small amount of illite, kaolinite, elo stone, chlorite, zeolite, quartz, feldspar, calcite and so on. It is white, flaxen commonly, because contain iron content how much to show again shallow ash, shallow green, pink, brown red, brick red, gray black, have waxy, soil-shaped or grease burnish. Montmorillonite minerals belong to monoclinal crystal system, some are loose as soil, some are dense and hard. Main chemical composition is sio2, 3 oxidation 2 aluminium and water, and also contains iron, magnesium, calcium, sodium, potassium and other elements, Na ₂ O and CaO content on the physical and chemical properties of bentonite and technology performance influence is quite big. Bentonite has strong hyposensitivity and expansibility. It can absorb 8~15 times the water volume of its own volume, and the volume can expand several times to ten times.

The ore of Xinyang Shangtian bentonite in Henan province is calcium bentonite, whose performance is slightly worse than that of sodium bentonite. The main mineral composition is calcium montmorillonite, with 40%~70% content. Other associated impurity minerals are mainly calcareous, containing 20%~30%. There are also small amounts of calcite, illite, siderite, and organic matter. Calcareous montmorillonite has a fine grain, mostly 1~3 m. The particle size of the main impurity mineral calcarenite is 0.1~0.5 m, which is evenly distributed and has a close symbiotic relationship with montmorillonite. Compared with the ideal montmorillonite structure composition, the SiO ₂ and Si: Al molecular ratio are obviously on the high side, the Al ₂ O ₃ is relatively low, excess silica that exist.

The basic properties of bentonite include blue absorbance, cationic exchange amount and component, colloidal value, expansion capacity, pH value, etc.

Process performance test items are determined according to their purpose, and common ones include:

(1) Mechanical manufacturing: wet compressive strength, dry compressive strength, hot wet tensile strength, air permeability;

(2) Metallurgical pellets: compressive strength, falling times, bursting temperature, water absorption of 2h and 24h;

(3) Drilling mud: pulp making rate, water loss rate, viscometer reading, plastic viscosity, wet screen analysis, etc.;

(4) Petrochemical industry: decolorization power, specific surface area, free acid, activity, moisture, particle size, etc.

According to the use, bentonite should be tested as follows:

(1) Water absorption. Bentonite can absorb 8~15 times of its own volume of water. After absorbing water, the volume expands, and the volume can expand several times or a dozen times. The water absorption of bentonite is expressed by water absorption rate and water absorption ratio. The quality of water adsorbed by a unit mass of bentonite is called water absorption rate (%), expressed as a percentage. In the initial stage, it increases with time and finally reaches saturation. The percentage of water absorption in the first 10min and 2h is called water absorption ratio.

(2) Expansion volume. The expansion capacity of bentonite in dilute hydrochloric acid liquid is expressed as expansion capacity. The expansion capacity of sodium bentonite is higher than that of calcium bentonite and acid bentonite. Bentonite of the same property, the more montmorillonite, the higher the expansion capacity. Expansion capacity is one of the technical indexes to identify the properties and quality of bentonite ores.

(3) Adsorption decolorization. Bentonite has certain adsorption capacity for various gases, liquids and organic substances, and the maximum adsorption capacity can be up to 5 times of its own mass. In particular, acidic bentonite and active clay activated by acid treatment have good decolorization performance for various oils.

(4) Colloidal valence. Bentonite can be dispersed into colloidal suspension in aqueous medium. The suspension has certain viscosity, thixotropy and lubricity, which are characterized by colloidal value.

(5) Adhesion and plasticity. The admixtures of bentonite, water, mud or sand, etc., are adhesive and malleable, and are generally expressed in wet compressive strength (wet compressive strength) and hot wet tensile strength. The wet compressive strength was used to evaluate the wet bonding ability of bentonite.

(6) Pulping performance. One of the main indexes to measure the pulping performance of bentonite is the pulping rate, that is, the volume number (m /t) of the suspension with apparent viscosity of 15Pa·s can be prepared per unit mass of bentonite.