Pure silver is silvery white, so it is also called silver. Among all metals, silver has the highest electrical and thermal conductivity, good ductility and plasticity, is easy to polish and shape, and can form alloys or pseudo-alloys with many metals. Silver also has strong resistance to corrosion, organic acids and alkali, and is not easily oxidized under ordinary temperature and humidity. Because silver has so many advantages, it has not only been used as currency, ornaments and utensils for a long time, but has also been widely used in modern industry, becoming an indispensable and important raw material for industrial and national defense construction.
1. Characteristics of mineral raw materials
Currently, it is known that there are more than 200 silver minerals and silver-containing minerals in which silver exists in the form of major elements, minor elements and indefinite amounts. Among them, silver There are more than 60 kinds of silver minerals and silver-containing minerals as the main element, but they have important economic value. As the main raw materials for silver production, there are 12 kinds: natural silver (Ag), silver-gold ore (AgAu), and albite (Ag2S). , dark red silver ore (Ag3SbS3), dark red silver ore (Ag3ASS3), horny silver ore (AgCe), brittle silver ore (Ag2SbS3), antimony silver ore (Ag3Sb), selenium silver ore (Ag3Se), tellurium silver ore (Ag2Te ), zinc-antimony harzburgite (5Ag2Sb2S3), sulfur-antimony copper-silverite (8 (AgCu) SSb2S3).
Silver is a copper-type ion, sulfur-loving, and has strong polarization ability. It often exists in the form of natural silver, sulfide, sulfate, etc. in nature. Because of its large ionic radius, it can form selenide and telluride with huge anions Se and Te. But it usually likes to hide in galena, either mechanically mixed or as isomorphic latent crystals. Secondly, it occurs in minerals such as natural gold, turbid copper ore, chalcopyrite, and sphalerite. Therefore, silver can often be recovered during the mining and smelting processes of lead-zinc mines, copper mines, and gold mines.
In the endogenous process, silver tends to be highly concentrated in the hydrothermal stage, enriched into silver (gold) or various silver-containing polymetallic sulfide deposits; under supergene conditions, silver Sulfide can form Ag2SO4, which has a certain solubility and is easily soluble in water, and forms secondary enrichments in the lower part of the oxidation zone; during deposition, silver often migrates together with copper, gold, uranium, lead, zinc or vanadium, phosphorus, etc. , precipitated in sandstone, clay shale and carbonate rocks. When it reaches a certain degree of enrichment, it can form sedimentary or layer-bound silver deposits; during the process of metamorphism, it is finely dispersed in the original rock. The silver, through the extraction and activation migration of metamorphic hydrothermal fluids, can be enriched under appropriate geological conditions to form new deposits with economic value, or the original ore bodies can be superimposed and enriched.
Due to the wide variety of silver minerals or silver-containing minerals, which can be formed at different stages of geological processes, these silver minerals are often distributed in different mineral phases, and even several types of silver minerals occur in In the same ore, in addition to existing independently as coarse-grained single crystals and embedded in gangue minerals, they also appear as fine continuous crystals with galena, sphalerite, pyrite, chalcopyrite, etc., and some It exists in the above minerals in a dispersed state. This characteristic of the distribution of silver minerals brings certain difficulties to the design of ideal mineral processing techniques and processes. Therefore, technological research on silver minerals and primary minerals is of great significance for the optimal recovery of silver.
2. Uses and technical and economic indicators
For a long time, a large amount of silver with higher purity has been used to make silver coins and decorations. With the development of science and technology, silver has gradually shifted from traditional consumption in currency and jewelry and crafts to the application and development of industrial technology. At present, it has been widely used in electronics, computers, communications, military industry, aerospace, film and television, photography and other industries.
In the film, television and photography industries, because silver halide salts (silver bromide, silver chloride, silver iodide) and silver nitrate are particularly sensitive to light, they can be used to make movies, television and photography. The required black and white and color films, negatives, exposure and printing papers, photosensitive films for printing and plate making, X-ray films for medical and industrial flaw detection, and various special materials used in aerial surveying and mapping, astronomical space exploration and national defense scientific research, etc. Photosensitive materials.
In the electromechanical and electrical industry, silver is mainly used in the form of pure metal and silver alloy as electrical contact materials, resistance materials, solders, temperature measurement materials and thick film slurries. For example, electrical contacts made of silver-copper, silver-cadmium, silver-nickel and other alloys can eliminate the shortcomings of general metals such as consumption deformation, contact resistance and bonding; low-voltage power switches and lifting equipment made of silver-tungsten, silver-molybdenum, silver-iron alloys, etc. Switches, heavy-duty relays and electrical contact materials can be widely used in cutting-edge industries such as transportation, metallurgy, automation and aerospace. In the thick film process, silver paste is used earliest, has the best conductivity, and has strong adhesion to ceramics.
In the petrochemical industry, silver is mainly used in chemical reactions as catalysts such as Ag/Al2O3, KBr-Ag-Al2O3, and Au-Ag nets.
In the medical and health industry, silver, gold, silver mercury, silver-tin alloy, etc. are important dental materials; Yinbodan and Zhenxin Pills have the functions of calming the mind, nourishing the mind, and calming the internal organs; silver gauze and cotton wool can Treat malignant ulcers; silver wires and silver sheets are excellent materials for fixing broken bones and repairing skull holes. Silver salt has good bactericidal effect. Silverware has a special purpose.
In agriculture and meteorology, silver iodide is used for artificial rainfall.
In terms of energy utilization, silver is coated on a huge curved glass mirror to concentrate sunlight and convert it into heat and electricity. Silver-zinc and silver-cadmium batteries are more than 20 times stronger than ordinary batteries. In addition, silver-coated glass windows can prevent ultraviolet rays from passing through, saving energy consumption and costs of air conditioning equipment.
Since there were not many independent silver deposits discovered in my country before the 1980s, most of the silver was an associated (***) component of non-ferrous base metal ores, and was evaluated incidentally when exploring the main minerals. When the silver content is greater than 5~10g/t, the calculated reserves are given. If the dressing and smelting performance of silver is better, it is sometimes reduced to 1g/t in copper and gold ores, and 2g/t in lead-zinc ores.