Comprehensive utilization of fumed silica and asbestos tailings

1. Overview

Fumed Silica, also known as fumed silica, is a kind of fine nano-scale amorphous silica obtained by high temperature hydrolysis of halosilane in hydrogen-oxygen flame. It has small particle size, uniform particle size distribution, large specific surface area and high surface activity. Fumed silica is widely used in polymer composite materials, silicone rubber, coatings, electronic packaging materials, colloidal batteries, ceramics, plastics, glass fiber reinforced plastic, sealants, paper, food, cosmetics, gel coat resin, chemical mechanical polishing and other industries, can play a reinforcing, thickening, thixotropic, extinction and other roles.

The development of fumed silica in China began in the 1960 s. After 2006, the development of polysilicon industry related to photovoltaic has provided a rich source of raw materials for the development of fumed silica, and the whole industry has developed rapidly. Since 2012, due to the oversupply of the photovoltaic market and the economic situation at home and abroad, most of China's polysilicon manufacturers have fallen into a deadlock, resulting in a sharp decline in silicon tetrachloride in the market, thus affecting the production of fumed silica production enterprises. Fumed silica production plants are generally underoperated, and some enterprises are in a state of shutdown or partial shutdown.

In 2012, the total production capacity of fumed silica in China was 97400t/a, with an actual output of 52300t t. Among them, the production capacity of Chinese-funded enterprises is 52400t/a, and the actual output is 19300t/a; The production capacity of foreign-funded enterprises is 45000t/a, and the actual output is 33000t/a.

In 2016, the total production capacity of fumed silica in China will reach 137000t/a, the actual output will be about 80000t/a, and the operating rate will be about 60%.

2. Market Analysis

1, Consumption

The apparent consumption of fumed silica in 2016 is about 60000 t, of which fumed silica for rubber and sealing materials accounts for about 64% of the total consumption and is mainly used as a reinforcing agent. Fumed silica for electronics, electricity and polyester products accounts for about 17%, mainly used as reinforcing agent and flow aid; coating ink, photosensitive materials with fumed silica accounted for about 13%, mainly used as a dispersant, anti-settling agent, matting agent; other uses fumed silica accounted for about 6%.

2, Variety and Quality

Domestic fumed silica production enterprises produce 150, 200, 300 and 380 series products. In addition, there are compressed fumed silica (150P, 200P), highly transparent fumed silica products (150H), special fumed silica for colloidal storage batteries (200B), and hydrophobic fumed silica series products. Hydrophobic product treatment agents include dimethyldichlorosilane and hexamethyldisilazane.

At present, the specific surface area of domestic fumed silica products can be well controlled within the requirements of the national standard, but compared with imported products such as Japan, South Korea, Germany, and the United States, the specific surface area uniformity is poor. The transparency of high-temperature silicone rubber made by domestic fumed silica is poor, the tensile rate is low, and other physical properties basically meet the requirements.

3, Market Situation

In recent years, the fumed silica market * * * * * * has shown a downward trend, from 3.5~55000 yuan/t in previous years to 2.5~35000 yuan/t now. Although the market price of fumed silica is higher than that of precipitated silica, the production cost is high and the market capacity is small. At the same time, the application of fumed silica in coatings, matting agents, pharmaceuticals, and tire industries has been replaced by relatively cheap chemically modified precipitated silica and highly dispersed silica, and the market space has been compressed.

3. production of fumed silica from asbestos tailings

The main chemical composition of asbestos tailings is silicon, magnesium, iron, nickel and other valuable elements. Theoretically speaking, it is feasible to use silicon in asbestos tailings to produce fumed silica, and it is also a good way to use silicon in asbestos tailings. However, the separation and extraction of silicon from asbestos tailings to produce fumed silica should pay attention to the following three key issues:

1, technical sources and ****** issues. At present, there are few studies on the direct production of fumed silica from asbestos tailings. Although the patent application published No. CN101250622A proposes a comprehensive treatment method for the whole wet process of serpentine ore, the silicon product produced by the method is the gas phase white carbon black. However, it is understood that the process has not been able to pass the pilot study and obtain industrial application, and its maturity and ****** nature should be carefully investigated and verified.

2, resource utilization level and environmental protection issues. Asbestos tailings are hazardous solid waste, and their comprehensive utilization should be based on the premise of full element, high level utilization and no secondary pollution. Although the patent application with the open number CN101250622A puts forward the comprehensive treatment method of the whole wet method of serpentine ore, but after the analysis of the literature, it is confirmed that the iron concentrate obtained by the process is a mixture of ferrous hydroxide and iron hydroxide, the iron grade is not high, and there are problems such as serious loss of magnesium and nickel in the process of iron precipitation. This situation will affect the level of comprehensive utilization of valuable resources in asbestos tailings. At the same time, the comprehensive utilization of magnesium carbonate mother liquor adopts the method of evaporation, concentration and recovery of ammonium sulfate, which has some problems, such as high energy consumption, inappropriate control of treatment cost, insufficient purity of ammonium sulfate and low added value. The recovery of ammonium sulfate will greatly reduce the economic benefits of the comprehensive utilization of asbestos tailings due to its serious losses. In addition, the decomposition method described therein cannot effectively ablate the short asbestos fibers in the asbestos tailings, which are mixed with the leaching tailings, and the so-called use of the tailings for the manufacture of cement or tiles will not be achieved.

3, construction scale problem. Fumed silica is a fine chemical with high value but limited market capacity, belonging to small tonnage products. For the comprehensive utilization of asbestos tailings, the construction scale and processing capacity are often large, and the yield of white carbon black is high. If the production of fumed white carbon black, then the production will be too large to make the enterprise in the production after the market bottleneck. Taking asbestos tailings in Asbestos County, Sichuan Province as an example, its SiO2 content is 42%. If a production plant with an annual processing capacity of 100000 tons of asbestos tailings is invested and the SiO2 yield is considered at 90%, more than 36000 tons of fumed silica can be produced each year, which will make the total production capacity of fumed silica in China increase by 26.3 on the basis of 137000 tons in 2016. It will not only cause a major impact on the already surplus fumed silica market, but also make the production enterprises fall into the dilemma of poor product sales from the date of production.