Analysis of technical conditions for resource utilization of perlite tailings

I. Introduction

In China's Henan, Northeast, Inner Mongolia, Hebei and other places are rich in perlite mineral resources, only Henan Xinyang Shangtian ladder reserves of more than 100 million tons. The development and utilization of China's expanded perlite has been 30 years old, with an annual output of 6 million m 3 . However, most of the ore used in China's perlite industry is medium and coarse sand. A large amount of fine sand of less than 60 mesh is discarded as tailings, and a large part of the resources are not fully utilized. Practice has proved that this part of the fine sand happens to be a suitable raw material for the production of spherical closed-cell expanded perlite, and the processed product has better performance.

Spherical closed-cell expanded perlite is a new type of thermal insulation material, mainly used in building insulation and energy saving and industrial lightweight materials. Compared with traditional expanded perlite, it has low water absorption, high strength, good mortar flow performance and production. Significant advantages such as process environmental protection. The key processing technology is the self-designed electrothermal expansion furnace. Because of the radiant heat and no open flame, there is no updraft, so the expanded perlite powder can be taken from the lower part of the expansion chamber (furnace tube). In order to facilitate the direct grading of the product, the whole process is free of dust and noise, and there is no waste discharge. The detailed structure of the device has been reported and will not be described in detail herein.

Second, the formation principle of spherical closed-cell expanded perlite

In the traditional production process of expanded perlite, the preheated ore directly enters the furnace, the flame temperature is as high as 1400 ° C, and the residence time of the particles in the expansion chamber is short, about several to several tens of microseconds, when the particles are heated to a plastic state, wherein The water suddenly evaporates and breaks through the surface of the particles, and the resulting expanded particles carry a large number of bursting cracks and cracks, that is, open-cell structures. In the electrothermal spherical closed-cell perlite production process, the temperature is zone-controlled, the temperature in the heating zone is relatively uniform, the peak temperature is low, and the heating direction is perpendicular to the flow direction of the raw material; the residence time of the particles in the expansion zone is long, which is 5~ 20s; the ore particles expand in a progressive manner in the expansion chamber. During the expansion process, the uneven portion of the surface of the particles is softened, and the surface tension becomes smaller after softening. When rolling, the concave and convex portions of the surface of the particles are softened and filled, and the shape is also increased. The rules of the coming and going, gradually forming a spherical closed-cell structure.

Third, the main ore properties of perlite tailings

Henan Xinyang Perlite reserves the first in the country, with an annual output of 121.36 million tons and an annual output of 311,700 tons. It is an acidic volcanic eruption. The ore is collected from the tailings discarded from the Yangjiawan-Liujiachong mining area in Xinyang, Henan Province. Its composition is stable and it is pure perlite. The rock is early Cretaceous acid lava, glassy crystal structure, pearl or block structure, mainly composed of volcanic glass. Composition, a small amount of translucent feldspar and quartz acicular crystals can be seen under the microscope. The chemical composition (%) was: SiO 2 71.82; Al 2 O 3 12.37; Na 2 O 3.55; K 2 O 4.69; CaO 0.83; Fe 2 O 3 0.79; MgO 0.19; loss on ignition 5.76.

Fourth, analysis of processing technology conditions

According to the principle of the formation of spherical closed-cell expanded perlite, after years of research, our institute has developed a perlite tailings electric heating furnace. The process is dry-sieving-preheating-heating-grading. The main factors affecting the production of spherical closed-cell perlite include raw material particle size, tailings water content, feed amount, electric heating temperature and so on.

(1) Influence of raw material particle size

Three groups of different sizes of ore sands were selected from 20 to 60, 60 to 260, and 260 to 325 mesh for expansion experiments. The experimental results are shown in Table 1. It can be seen from Table 1 that the 60-260 mesh ore (ie, perlite tailings) has the best expansion effect, and the product has the highest sphericity and closed cell ratio. The 20-60 mesh ore with coarser raw material content has the lowest bulk density after electrothermal expansion, but the sphericity and closed cell ratio are not ideal. The reason is that it is difficult to control the particles through the softening point temperature in a short time when the ore particle size is large. The outer surface is uneven and the corner portion is eliminated. It can be seen that the grain size of Xinyang Perlite tailings just meets the particle size requirements of the raw materials. Moreover, the shape of the ore is regular, and the shape of the spherical and square is the best, and the quality of the expanded product is superior.

Table 1 Experimental results of electrothermal expansion of different granularity perlite ore

(2) Impact of ore water content

The water content in the perlite tailings exists in two forms: one is the fissure water attached to the rock particle cracks, which generates a large vapor pressure at high temperatures and causes the particles to burst, increasing the powdering rate of the product. To avoid this phenomenon, it must be removed by preheating; the other is the combined water that remains in the vitreous when the magma is sprayed out of the ground or in the process of mineralization, which is the main cause of the expansion of perlite. The preheated tailings require a certain water content, which is the residual water content. The residual water content required for the expansion of traditional perlite is controlled at 2% to 3%. Due to the special beading of the process, the tailings cannot be heated during the heating process. More water evaporates, so the amount of residual water cannot be too much, otherwise the vitrified layer on the surface of the particles is difficult to form or the outer shell of the particles is too thin, and the particles may burst or fail to expand, resulting in excessive or too small product bulk density. Experiments have shown that it is most suitable to control the water content of spherical closed-cell perlite from 1.5% to 2%. The residual water content can be controlled by the preheating temperature and the warm-up time. The tailings preheating is carried out in a preheating furnace. At a temperature of 300-600 ° C, the tailings are heated for about 30 minutes to obtain a relatively ideal puffed raw material. However, it should be noted that the preheating temperature and the preheating time must be controlled and coordinated. When the temperature is high, the preheating time is about 12 minutes. When the temperature is lowered, the preheating time is relatively extended. The specific operation needs to be based on the test results of residual water content. However, below 300 ° C or higher than 600 ° C, the ideal preheating effect is not achieved.

(III) Temperature control of electric heating puffing furnace

Preheating the ore into the furnace cannot be directly subjected to the peak high temperature, otherwise it will suddenly burst into porous particles. The processing expansion furnace is an electric heating vertical puffing furnace, the heating method is implicit protection heating, the ore is not in contact with the bright flame, and the furnace temperature is set from top to bottom, and the ore is gradually heated after entering the furnace, first softening and then expanding. When softened and rolled down, the surface tension becomes smaller due to the smaller surface viscosity of the particles, and there is a natural ball forming process. The furnace temperature control is determined by the nature and particle size of the tailings, generally 400-1300 ° C, and the heating time of the materials in the furnace is 5-20 s. Taking the white material of Xinyang District of Henan Province as an example, the particle size is 80-200 mesh, and the heating temperature rise curve is shown in Figure 1. It can be seen from Fig. 1 that each temperature zone of the electric heating puffing furnace has a certain constant temperature range, and the temperature transition between the adjacent two temperature zones is stable, and there is no significant peak temperature, thereby avoiding the bursting of the perlite expansion process. The test results of the processed products show that the mineral sand expansion rate is 94.5%, the product bulk density is 110-145kg/m 3 , and the particles are basically spherical closed-cell structure. It can be seen that temperature control is a key factor in improving the sphericity, the closed cell ratio, and adjusting the bulk density of the product.


(4) Feed volume control

Fig.1 Temperature rise curve of spherical closed-cell perlite processing

The feed amount is directly related to the electric furnace power, the furnace area, the mineral sand variety, the grain size and the puffing effect. When the power of the electric furnace is constant, the excessive feed amount will cause the temperature to be less than compensated, resulting in a large product density, that is, the expansion effect is not good; when the feed amount is small, energy is wasted, the output is too low, and the cost is too high. The actual production shows that under ideal preheating conditions, uniform feeding and good dispersion can improve product quality and save energy. A suitable feed rate should be 120 kg/h.

V. Conclusion

The processing of spherical closed-cell expanded perlite can use a large amount of perlite tailings as raw materials, turning waste powder discharged from mine into waste, and effectively improving resource utilization. The spherical closed-cell expanded perlite obtained by the above method is compared with the performance of the traditional porous product (see Table 2), and its density is stable, the water absorption rate is low, the strength is high, and the mortar fluidity is good, except that it cannot replace the traditional in adsorption filtration. In addition to products, it can replace traditional products in the field of heat preservation, energy saving and light building materials and fillers. The market potential is huge, and China's perlite deep processing technology can be raised to a new level. In order to build a project of spherical closed-cell expanded perlite with an annual output of 800,000 m 3 and an installed capacity of 900 kW, the total investment is about 36 million yuan. After the completion of the project, the annual consumption of perlite tailings is 50,000 tons, which can generate sales revenue of about 48 million yuan. / Year, the profit and tax will be 22 million yuan / year, the sales profit rate can reach 37%, the investment profit rate can reach 50%, and the investment recovery period is 1.8 years.

Table 2 Comparison of properties of spherical closed-cell expanded perlite and traditional porous products

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