Montmorillonite sodium modification process, equipment and common problems

Compared with calcium-based montmorillonite, sodium-based montmorillonite has better water dispersibility, suspension, swelling, thickening and lubricity, so it has a wider range of uses.

However, most of the bentonite ore produced naturally in China is calcium-based bentonite, and the commonly used method in the industry is to increase the expansion times of bentonite by adding modifier sodium treatment under certain conditions.

1. Montmorillonite sodium modification process and equipment

There are many processing methods for montmorillonite sodium modification, which can generally be divided into dry method, semi-dry method and wet modification.

Due to the difficulty of ion migration and poor modification effect under dry conditions, wet and semi-dry methods are used more, including stirring, ball milling, homogenization, extrusion sodium, etc., by increasing shear force, reducing dispersed particle size, prolonging aging time, etc., to speed up the ion exchange process, improve the reaction efficiency and reaction degree, so as to achieve the purpose of promoting the modification effect.

The most common laboratory modification is stirred sodium, montmorillonite and modifier are added at the same time as pulping, and sodium-based bentonite is prepared by dehydration, drying and crushing after soaking pulping, which is often used in combination with wet purification. This method has low requirements for equipment and easy to realize the process, but the linear speed of the stirring equipment is low, the shear force is small, although the ion exchange process is accelerated to a certain extent by water bath heating, the dispersed particle size of montmorillonite is relatively coarse, so the modification effect is limited, and the sodium is not sufficient.

Ball mill modification is through the high-speed rotation of the ball mill jar, driving the ball mill medium such as aluminum balls, zirconium balls, etc. to move together, due to the action of inertia and centrifugal force, it falls down to a certain height, and produces a strong impact on the grinding material; At the same time, the medium ball rotates and revolutionizes in the ball mill tank, and the extrusion impact force, shear force and friction force on the material are generated between the medium ball and between the medium and the ball mill tank, and the montmorillonite particles are finened under the joint action of these forces, and the completion of the sodium reaction is promoted. However, due to the influence of the speed of the ball mill jar, the size of the medium ball, the grinding limit, etc., the montmorillonite particle size modified by ball milling is finer than that of the stirred sodium sample, but coarser than that of the modified sample of colloidal mill.

Colloid mill and ball mill modification are both sodium modifications that achieve ultra-fine montmorillonite slurry. When the colloid mill is modified, the rotor and stator move at a relatively high speed, and the material is subjected to strong friction, shear, spiral impact and high-frequency vibration when passing through the gap between the two, so that the material is effectively mixed, dispersed, and ultra-fine. The general linear speed is 8-12m/s, and the processing particle size is finer than that modified by ball milling.

Due to the high cost of wet processing and drying, semi-dry sodium is more commonly used in actual production. Generally, after adding a certain amount of sodium solution to the raw ore, mix well, stack for 7-10 days, and often turn and stir, the sodium efficiency is low and the cycle is long. Modification can improve the ion exchange efficiency and shorten the sodium reaction time by applying a certain shear force at the same time, or using the microwave radiation process.

2. Common problems of montmorillonite sodium modification

Common sodium methods commonly have the following problems:

(1) The sodium time is long, and the reaction is incomplete. In actual production, calcium-based montmorillonite ore is generally sodified under the condition that the water content is greater than 10%, and montmorillonite contains a large amount of adsorption water and interlayer water, which hinders sodium ions from entering montmorillonite particles to a certain extent, and after the particle surface contacts the modifier sodium, a barrier layer is formed, and sodium ions are difficult to migrate into the interlayer, preventing the continuation of the ion exchange reaction, and the sodium is not sufficient, and the sodium time is longer. Generally, the barrier layer is broken by increasing extrusion or strong shear, and sodium ions are forced to enter the montmorillonite layer by external force to promote the ion exchange reaction.

(2) The ferric iron in the structure is not oxidized to ferric. The montmorillonite octahedral lattice is Al3+, and when Fe3+ replaces Al3+, it is electrically neutral. When Fe2+ replaces Al3+, it is negatively charged, and under the action of Coulomb force, the crystal layer is more tightly bonded, and the expandable crystal layer is less and the expansion is smaller. When the Fe2+ inside the montmorillonite crystal is oxidized to Fe3+, more overlapping crystal layers will be separated, and the proportion of expandable crystal layers will increase, which will improve the swellability.

On the one hand, under natural weathering conditions, the ferric iron in montmorillonite is slowly oxidized to ferric, and on the other hand, the sodium ions gradually enter the montmorillonite layer by prolonging the time, so as to promote the slow progress of the sodium reaction, but it is often placed for several months or even more than half a year, and the cycle is very long.