Environmental materials advocate green material technology, and natural minerals are a kind of materials with rich resources, low price and the best coordination with the environment. Bentonite, zeolite, diatomite, sepiolite, attapulgite and other natural non-metallic minerals also have the function of purifying and repairing the environment, so they are ideal environmental materials.
Compared with other environmental materials, the application of non-metallic minerals in the field of environmental protection has the following four characteristics: < br / > (1) a wide range of applications, in addition to the "three wastes" treatment, but also suitable for new pollution caused by the development of high technology, such as a variety of radiation, electromagnetic fields, low-frequency noise, etc. < br / > (2) non metallic minerals are natural, natural inorganic minerals, with symbiosis with the natural environment (3) most of non-metallic minerals can be recycled in environmental protection, without secondary pollution and low cost of pollution control; (4) non metallic minerals have natural self purification function, which can play a unique role in non-point source regional pollution problems that can not be solved by general environmental protection technology, That is, the geological and technical characteristics of environmental attributes of non-metallic minerals, which is unmatched by physicochemical and biological pollution control methods.
Therefore, the research and development of "resource-based" environmental protection mineral materials has broad development prospects, which can not only expand the comprehensive utilization of mineral resources, but also greatly reduce the cost of environmental pollution control, resulting in obvious economic and social benefits.
1. Bentonite < br / > bentonite is a kind of clay rock which is mainly composed of montmorillonite minerals. Due to its large surface area and adsorption capacity, various researches on the treatment of wastewater with bentonite have been carried out at home and abroad in recent years, especially on the purification of eutrophic water. China is rich in natural bentonite resources, so it is necessary to develop bentonite and modified bentonite water treatment Physicochemical agents have wide application prospects.
For organic pollutants, organobentonites have stronger adsorption capacity than other bentonites. In foreign countries, quaternary ammonium salt modified clay was used to remove malathion and butachlor from aqueous solution, and tetradecyltrimethylammonium bromide modified bentonite had the best effect, with the removal rates of 91.5% and 73.25% respectively.
Modified bentonite adsorption is a promising new method for phosphorus removal. Hu qiaokai and others used Al3 + to modify bentonite, and found that it had strong adsorption and removal effect on phosphorus. For the wastewater with phosphorus content less than 11 mg / L, the removal rate is more than 95.5%; the bentonite after adsorption treatment of phosphorus containing wastewater can also be used as agricultural fertilizer, which can not only provide phosphorus fertilizer for crops, but also improve the soil, realizing the recycling of waste and phosphorus.
2. Zeolite < br / > is a group of porous and hydrous aluminosilicate minerals with alkali or alkaline earth metal framework structure, which has good selective adsorption, ion exchange and catalytic properties, and has become one of the important environmental engineering materials. The United States and Japan have built a certain scale of natural zeolite wastewater treatment plants. Many achievements have been made in the application of zeolite in drinking water purification and industrial wastewater treatment in China. Using coal gangue, kaolin and bentonite as the main raw materials to produce synthetic zeolite, which can be used to replace sodium tripolyphosphate in traditional detergent, can greatly reduce the environmental pollution caused by residual phosphorus in washing wastewater.
In order to further improve the adsorption and ion exchange properties of natural zeolite, it is necessary to modify or modify natural zeolite. The modification of natural zeolite is mainly to change the type of cation in zeolite to improve its ion exchange and adsorption properties. < br / > zeolite has the following advantages in wastewater treatment: < br / > abundant reserves, low price and easy to obtain; < br / > simple preparation method; < br / > low cost and easy to obtain It can remove inorganic and organic pollutants in water; < br / > it has high chemical and biological stability; < br / > it is easy to regenerate.
3. Diatomite < br / > diatomite has unique pore structure, high porosity, light weight, large specific surface area and certain adsorption. In addition, the surface of diatomite is covered by a large number of silicon hydroxyl groups and hydrogen bonds exist. These - OH groups are the fundamental reason for the surface activity, adsorption and acidity of diatomite. < br / > due to its strong adsorption, diatomite can not only remove particulate and colloidal pollutants, but also effectively remove chromaticity and dissolved phosphorus and metal ions in the process of wastewater treatment. However, due to the low grade of diatomite in China, the content of diatom is low and the impurity content is high, so its application field is limited. In order to improve the effect of diatomite wastewater treatment, it is necessary to purify, activate, expand and modify the original diatomite. < br / > in addition, as diatomite is a kind of natural mineral, diatomite sludge has a large recycling space and good stability, which can be reused in agriculture, wastewater treatment, building materials and other fields after appropriate treatment.
4. Sepiolite < br / > Sepiolite is a kind of porous magnesium rich silicate clay mineral with low price and wide sources. The adsorbent prepared by activation has the advantages of high efficiency and renewable, which is a promising environmental material. Sepiolite has both neutral adsorption sites formed by silanol groups on the "outer surface" of silicate and negative adsorption sites formed by substituting low valent metal ions for si4 +. The distribution of these two sites on sepiolite makes it have strong adsorption capacity for neutral organic molecules or organic cations. Sepiolite not only can be used to adsorb organic cations, but also has been tried to adsorb organic anions in recent years, and achieved good results.
5. Attapulgite < br / > attapulgite, also known as palygorskite, is a kind of hydrous magnesium aluminum rich silicate clay mineral with chain layered structure. Because of its special structure, attapulgite has been widely used in building materials, mining, chemical fertilizer, food, pesticide, printing and dyeing, environmental protection and other fields, and is known as the "king of thousands of soils".
Attapulgite clay has the characteristics of abundant resources and low price in China, so attapulgite clay is more and more used as environmental mineral materials for adsorption treatment of various wastewater
Many researchers at home and abroad have explored the application of attapulgite as a natural cheap adsorbent in environmental protection. The application research scope of attapulgite adsorbent has been involved in indoor air and industrial waste gas purification, printing and dyeing, leather, electroplating, boiler iron and other industries wastewater treatment, domestic sewage, polluted wastewater and comprehensive wastewater treatment.
Source: Liang Kai. Application of nonmetallic mineral materials in environmental protection [J]. Geology and resources, 2011,20 (6): 458-46
