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Current Production Status and Application Prospects of Glauber’s Salt Liu Yunqin, Xu Tao (Glauber’s Salt Branch of Nanfeng Group, Yuncheng, Shanxi 044000) Abstract: Based on a series of objective facts and detailed data, this paper reviews the production history of Glauber’s salt. It analyzes, from a scientific perspective, the distribution, reserves, and mining conditions of this substance. By comparing the production processes of various manufacturers, it identifies suitable methods for producing Glauber’s salt using different raw materials. The market distribution of Glauber’s salt as well as the demand from various industries are also analyzed, providing a basis for further expanding its application areas, developing the market in a rational manner, and adjusting the product structure. This lays a foundation for the further development of Glauber’s salt. Keywords: Glauber’s salt; mirabilite; Resources 1 Raw material status 1.1 Distribution of mirabilite resources and production enterprises China has abundant mirabilite resources, with total reserves exceeding 10 billion tons, ranking first in the world. Manufacturers of sodium sulfate are located in more than a dozen provinces including Shanxi, Sichuan, Jiangsu, Xinjiang, Inner Mongolia, and Hunan, depending on the raw materials used; there are over 50 such manufacturers. The total production capacity for sodium sulfate is between 5 and 5.5 million tons per year, with an actual output of around 4.5 million tons per year. The amount available for market sale is 4.2 million tons per year, of which 900,000 tons are exported while the rest is used for domestic consumption. Calcium sulfate is a chemical product produced in large quantities, with a market price of only 300–400 yuan per ton. As a manufacturing enterprise, having only resource advantages is not sufficient; its geographical advantages, technical advantages, energy advantages, and policy advantages play a significant role in competition in the product market, with geographical location being the most important among them. For example, the mirabilite mineral resources in Qinghai account for 40% of the country’s total, but their development is restricted due to factors such as geographical location, mining methods, and production technology. Regions such as Sichuan and Jiangsu have become more advantageous production bases for sodium metabisulfite. The distribution of manufacturers is shown in Table 1. 1.2 Raw material structure and processing: The natural raw materials used for producing mirabilite fall into two categories: Glauber’s salt-type minerals and by-products from the salt industry. By-products of mirabilite include those derived from the production of synthetic fatty acids, rayon, and chromium-containing compounds; here, emphasis is placed on the natural raw materials in the form of Glauber’s salt-type minerals. Table 1 Distribution of China’s sodium sulfate manufacturers. Region (Province), Manufacturers, Capacity/(10,000 t•a-1): Sichuan – 23 manufacturers including Sichuan Tongqing Nanfeng Co., Ltd., with a total capacity of 228; Jiangsu – 4 manufacturers including Jiangsu Nanfeng Sodium Sulfate Co., Ltd., with a total capacity of 115; Shanxi – Shanxi Nanfeng Chemical Group, with a capacity of 50; Inner Mongolia – 6 manufacturers including Yikezhao League Chemical Industry Corporation, with a total capacity of 49; Xinjiang – 4 manufacturers including Xinjiang Salt Lake Chemical Plant, with a total capacity of 29; Hunan – 2 manufacturers including Xiangli Salt Mine, with a total capacity of 23; Gansu – 11 manufacturers including Gansu Yasheng Group, with a total capacity of 26; Qinghai – Lenghu Chemical Plant, with a capacity of 3. Total: 52 manufacturers with a combined capacity of 523. There are 3 types of natural gypsum deposits that contain sodium sulfate in nature, and all of these types have been identified and exploited in China. The first category consists of mirabilite deposits found in Shanxi, Inner Mongolia, Xinjiang, Gansu, and Qinghai. These are sedimentary deposits from modern inland lakes, representing lake-bottom sediments of mirabilite and glauber’s salt. They exist mainly in the form of Na2SO4, Na2SO4•10H2O, or glauber’s salt, along with impurities such as chlorine, calcium, magnesium, natron, and sediment. To extract these minerals, water is used to leach out the Na+ and SO42- ions from the mineral layers, adjusting the concentration accordingly. Then, by taking advantage of seasonal changes, mirabilite crystals are collected, and at a certain temperature, the mirabilite is dissolved to produce nitric acid solution. Currently, most manufacturers use the production process of \"multi-effect evaporation, utilization of the secondary steam from the last effect for dissolving mirabilite, and conversion of waste heat into nitrate\" to produce crude nitrate solution, which helps to save some steam. However, due to the processes involved in the crystallization, production, and transportation of mirabilite, the production cycle for the raw material is long (once a year), the manufacturing costs are high, and the cost of raw materials accounts for about 40% of the total production cost of mirabilite. These types of mines were the first to be discovered and exploited; there are the most manufacturers of this kind (over 25), but their scale is generally small. Many manufacturers in Gansu have an annual production capacity of 10,000 tons, while those with a larger scale include Shanxi Nanfeng Chemical Group and Gansu Yasheng Group. The second type of ore consists of solid gypsum deposits found in provinces such as Sichuan and Guangxi. The ore contains 25%–50% (by mass) of Na2SO4, 27%–30% of CaSO4, along with small amounts of MgSO4, NaCl, Al2O3, Fe2O3, and water-insoluble substances. Over the years, the relatively economical and less polluting \"underground chamber dissolution method\" has been used to produce crude nitric acid solution; production is not restricted by seasons. However, the costs associated with mining are high, with mine investment accounting for about 50% of the total cost. The calcium content in the crude nitric acid solution is around 2.5 g/L, and it is necessary to remove calcium and magnesium using two-alkali processes before it can be used. The density of this nitric acid solution is low, at only 0.90–0.93 kg/m3. The payback period for the mine investment is long, and raw material costs make up 30% of the total production costs. Currently, nearly 20 manufacturing enterprises in Sichuan produce about 2 million tons of calcium sulfate per year to supply the provinces in southwestern China. The third category consists of sulfate-rich underground mirabilite deposits found in the Jiangsu region; its main component is Na2SO4, with impurities such as NaCl and small amounts of calcium and magnesium, and very little water-insoluble material. It differs from surface brine, intercrystalline brine, and underground brine; its ore layer is relatively thick (on average 15 m), with a Na2SO4 content of over 80%. Due to its deep burial depth (around 2,000 m), mirabilite dissolves easily. The crude nitrate solution is produced by injecting water into connected wells. Although the initial investment for mining such deposits is high – a well capable of producing 100,000 tons per year of mirabilite requires an investment of 10 million yuan, and its service life is only 1–2 years – the mineral utilization rate is low. The international recovery rate ranges from 25% to 30%, while in China it is only 15%. However, the flow rate of the nitrate solution remains stable at 60–70 m3/h, and the quality of the crude nitrate solution is good, with a Na2SO4 content of around 320 g/L. The production cost of the raw materials is relatively low, accounting for only 25% of the total cost of producing mirabilite, making this a mineral resource with considerable potential. The mine was discovered in the 1980s and put into operation in the 1990s. It generally operated on a large scale, with high investment in equipment and a high level of automation, resulting in generally good economic returns. 2 Production technology status: Natural raw materials around the world share certain common characteristics, and as a result, the production processes for mirabilite also have some commonalities. Whether it is mirabilite deposits, sodium sulfate-rich brine from wells, or mirabilite produced as a by-product of chemical processes, all employ a two-step process: first, mirabilite or its aqueous solution is isolated, and then the refined raw materials are processed into the final product. The large-scale production of sodium sulfate in our country began in the 1950s, using mirabilite as raw material. The production methods include the melting method, the melting-evaporation method, the salting-out method, and the complete dissolution-evaporation method. In terms of design, it has evolved from the \"flat-pan method,\" \"flame tower method,\" \"single-effect evaporation,\" \"natural circulation,\" and \"vacuum evaporation\" to \"multi-effect vacuum evaporation with forced circulation.\" Through years of production experience and continuous technological upgrades, the production process for calcium sulfate has become more mature, with the production equipment being largely finalized. As various industries raise their requirements for the quality of meta-nitrate sulfate products, manufacturers currently use the \"complete dissolution evaporation\" dehydration method in their production processes. The evaporation process varies depending on the structure of the raw materials. There are vacuum evaporation production methods such as the “four-effect countercurrent waste heat nitration” process represented by Yuncheng in Shanxi, the “five-effect countercurrent” process represented by Sichuan, and the “five-effect cross-current” process used in places like Nanfeng in Jiangsu. The evaporation equipment mainly consists of “external heat forced circulation evaporators”; a few manufacturers use “internal heat forced circulation evaporators”, but due to factors such as production volume and energy consumption, the latter are trending toward being phased out. Centrifugal drying equipment is relatively consistent, with hydrocyclones and continuous feed horizontal centrifuges being used, along with air flow dryers, ensuring that the products meet relevant standards. For years, the packaging process has involved weighing with scales and manual packaging; in 2001, the Fourth Glauber’s Salt Factory in Yuncheng, Nanfeng, Shanxi, was the first to adopt automatic packaging and weighing technology, which effectively solved problems such as measurement errors in products, high labor intensity for workers, and environmental pollution. The results of this application were good, and it is now being promoted further. 3 Development of sodium sulfate monohydrate 3.1 Pursuing product refinement driven by the market Sodium sulfate monohydrate has been produced in accordance with the GB6009 - 92 standard for anhydrous sodium sulfate**. In recent years, as the market has shifted from a planned economy to a market economy, people’s living standards have continued to improve, leading to higher demands for everyday items such as laundry detergent, bathing products, printed materials, and glass. As raw materials for these products, domestic and international customers have an increasing demand for refined gypsum, with annual consumption reaching tens of thousands of tons. Gypsum variants with a calcium and magnesium content of 0.015%, “low-calcium and magnesium” gypsum; “high-purity” gypsum with a chloride ion content of 0.08%; “neutral” or “low-pH” gypsum with a pH level between 6 and 8; and “large-grain” gypsum with 75% particles larger than 150μm have all been produced and are used in various industries. The production processes for these gypsum variants are relatively mature, and their production costs are reasonable, enabling transition to large-scale production. 3.2 Introduction of modern equipment to improve production efficiency: With the development of science and technological advancements, efficient and energy-saving process technologies are increasingly being adopted in the production of calcium sulfate. For example, variable frequency drives are installed on circulation pumps, centrifuges, and fans, allowing the speed to be adjusted automatically according to the load level. This results in smoother equipment operation, reduced current consumption, more reliable process control, and energy savings of around 30%. The materials used for evaporation equipment and pipelines are gradually being replaced from carbon steel with stainless steel or titanium, which increases the whiteness of the product and reduces its iron content. Automatic monitoring and control systems are used for adjusting the liquid level in the evaporation tanks, improving the accuracy of level control, reducing the workload on workers, and preventing equipment failures caused by accidental or human factors. Furthermore, the use of new equipment and technologies such as \"pH automatic controllers\", \"two-stage feeding centrifuges\", and \"automated metering in the packaging process\" in the production of neutral alum creates significant benefits for enterprises, and it also reflects the continuous progress in alum production. 3. 3 The development and changes of mirabilite from national standards The first standard related to mirabilite was issued in 1959; it referred to the standard for \"sodium sulfate\", with the standard number HGB3045-59. Subsequent revisions were made, and corresponding standards were introduced. Firstly, the grading system was refined, with Class I premium products added (Na2SO4 ≥99.3%), to meet the needs of users with higher requirements. The pH parameter has been removed, reducing the need for manufacturers to adjust the pH level. Due to the differences in raw materials used across different regions, the pH of the products varies naturally. Moreover, not all users require neutral alumina with a pH of 6–8; by eliminating the need to control the pH level, production costs can be reduced. The requirement regarding product residues has been removed. There are many factors that affect the particle size of the product, such as impurities in the raw materials, the pH of the solution, the structure of the evaporator, the drying equipment, the process flow, and the process operation parameters. Any change in any of these factors can result in a change in the product’s particle size. When producing calcium sulfate, manufacturing can be carried out based on whether the customer has such a requirement, which provides more room for coordination between the manufacturer and the customer and is beneficial for the development of the enterprise. National standards are revised approximately once every 10 years, and this process takes a long time. Therefore, various companies have developed their own corporate standards for certain products, based on the needs of specific users and their own production conditions; examples include corporate standards for \"high-purity anhydrous sodium sulfate\" and \"low-calcium, low-magnesium anhydrous sodium sulfate\". 4 Overview of Product Applications 4.1 Market Distribution of the Product Sodium sulfate is a basic chemical raw material that is widely used in various sectors of the chemical industry. For example, it is used in the papermaking industry to compensate for the loss of alkali and sulfur during pulp production; about 40% sodium sulfate is added in the manufacture of synthetic detergents as a carrier for laundry powder; in the dye industry, sodium sulfate serves as the main raw material for producing sodium sulfide. At the same time, sodium sulfate is widely used in industries such as glass, printing and dyeing, textiles, leather processing, mining, and pharmaceuticals. In the past 2 years, China has added approximately 1 million tons of new capacity for producing sodium sulfate, and this growth rate reflects the increasing demand. At present, the production facilities for sodium sulfate are well-located, and the sales market is largely saturated. After joining the World Trade Organization, export volumes have increased, leading to a rise in overall demand. The applications of sodium sulfate in various industries are shown in Table 2. 4.2 Application Development Like all chemical products, the use of sodium sulfate has also evolved gradually. In 1987, researchers discovered that adding a certain amount of sodium sulfate to the feed of poultry, pigs, dairy cows, and other livestock had significant effects on increasing egg production in chickens, body weight in pigs, disease resistance in cattle, and milk production in dairy cows. This discovery was quickly adopted and widely applied. Sodium sulfate can also be used as a carrier for certain drugs intended for poultry and livestock. Currently, nearly 10,000 tons of sodium sulfate are used each year as a feed additive. In 1988, it was discovered that by using sodium sulfate, silica sand, and coal powder as raw materials and carrying out high-temperature melting reactions, water glass could be produced. This discovery changed the traditional method of producing water glass from soda ash, thereby reducing its production costs. After the 1990s, the use of sodium sulfate evolved toward more refined applications: high-purity sodium sulfate is used in the printing and dyeing industry, large-grained sodium sulfate is employed in the glass industry, and ultra-fine grades of sodium sulfate are used in the pharmaceutical industry, among other applications. Of course, some studies need to be put into practical use before their value can be demonstrated and they can be widely applied. Table 2 Applications of sodium sulfate in various industries Industry Consumption amount/(10,000 t•a-1) Share/% Synthetic detergents 155 36.9 Dyeing and printing 55 13.1 Alkali sulfide 45 10.7 Glass industry 40 9.5 Sodium sulfide 20 4.8 Barium sulfate 10 2.4 Other uses such as pharmaceuticals and feed 5 1.2 Export volume 90 21.4 Last edited by zxh6267 on 2009-3-24 11:16]