Methods and schemes of ore enrichment
During enrichment, ore undergoes mechanical processing, so the minerals do not change their basic chemical properties and composition during the process, in contrast to pyro- and hydrometallurgical processes, which are associated with chemical transformations of the components of the original raw materials.
The ore entering the beneficiation plant undergoes sequential processing in processes that, according to their purpose, are divided into preparatory, beneficiation proper and auxiliary (Fig. 1).
Preparatory processes
The main task of preparatory processes is to prepare the ore for enrichment. This preparation includes, first of all, operations to reduce the size of pieces - crushing and grinding and the associated classification of ore by size using screening and classification methods. The final size of the crushing is determined by the size of the mineral grains, which must be maximally open and free from intergrowths with minerals of the host rocks and the type of the main enrichment process.
Fig. 1. Enrichment stages.
Preparatory processes also include disintegration and washing processes, which are widely used in the preparation of sands from clay-containing placer deposits. As a result of these processes, in combination with classification and desliming, washed sands are separated, which are usually used for enrichment by gravity methods. The processes and methods of enrichment of minerals are based on the technological properties of the minerals that make up the ores. These include primarily density, mechanical properties (hardness and elasticity), magnetic and electrical properties, radioactivity, physicochemical, chemical and thermochemical properties.
Fig. 2. Qualitative enrichment scheme.
Most enrichment processes are carried out in an aqueous environment and the resulting products contain a large amount of water. Metallurgical plants, as a rule, accept concentrates with a moisture content of no more than 4-5%. Therefore, there is a need to dehydrate the resulting concentrates, and sometimes the tailings. Dehydration processes, including thickening, filtration and drying, are auxiliary processes. They can also include the process of dust removal, purification of circulating and waste water.
When enriching minerals, various process schemes are used, the choice of which is determined primarily by the material composition of the ore, the enrichment process used, and the requirements for the technological indicators of enrichment - the quality of concentrates and metal extraction. Very rarely in enrichment practice is it possible to obtain a conditioned concentrate and waste tailings. This is achieved only with a sequential combination of several enrichment operations. According to their purpose, enrichment operations are divided into main, cleaning, and control operations. For example, main flotation , control flotation, and cleaning flotation.
The main operation is the first enrichment operation in the cycle, as a result of which rough or coarse concentrate and tailings are separated. In the same scheme there may be several main operations, for example, in the enrichment of copper-zinc ore: main copper flotation, main zinc flotation.
Control operation – an operation of enrichment of tailings of the main operation with the purpose of additional extraction of valuable minerals from them. In the control operation, the concentrate is an intermediate product, which is usually returned to the main operation, and the tailings are waste.
Cleaning operation – an operation of repeated enrichment of concentrates of the main operation with the purpose of increasing the quality of the concentrate. In this operation, tailings are an intermediate product, which is also returned to the main operation.
The qualitative diagram (Fig. 2) gives an idea of the enrichment method, the stages of the process, the number of cleaning and control operations, the adopted method of processing industrial products and the quality of the final enrichment products.
The circuit diagram of the apparatus is a graphic representation of the movement of ore and enrichment products according to a diagram with conventional images of the apparatus, indicating the type and number of machines and apparatus (Fig. 3).
Fig. 3. Scheme of the circuit of devices for ore enrichment.
1 - feed ore bin; 2, 5, 8, 10, 11 - conveyors; 3,6 - screens; 4 - jaw crusher; 7 - cone crusher; 9 - crushed ore bin; 12 - mill; 13 - spiral classifier; 14 - flotation machine; 15 - thickener; 16 - vacuum filter; 17 - drying drum.
