1. Steps of the gravity concentration process
The gravity concentration of ore is also carried out in a series of continuous operations, just like other mineral processing production. By the nature of the operation can be divided into three major parts: preparation operations, separation operations and product handling operations.
1. Preparation operations
The preparation operations for gravity concentration mainly include
(1) Crushing and grinding to liberate the minerals.
(2) Washing and desliming of the ore cemented by clay.
(3) The use of sieving or hydraulic separation method for the selection of raw materials according to the size classification, and then the raw materials are selected separately.
The latter preparatory operation is a specific requirement for gravity concentration, because in general gravity concentration equipment, the sorting conditions are most suitable only for a specific particle size.
2. Separation operations
Separation operation is the main part of the sorting minerals, also according to a certain process, gravity concentration process combination of complexity is very different, but most of the process structure is more complex, this is due to
(1) Gravity concentration process methods have more options, different particle size of the ore should be selected for different process equipment.
(2) Even the same type of equipment, it should be selected for different operating conditions when dealing with different particle size for feeding.
Most of the gravity concentration equipment enrichment ratio or tailing capacity is not high, need to make several selections or sweeping to obtain the final product.
The advantage of gravity concentration lies in its ability to process ores of various sizes. From the gravity concentration point of view, the ore can be divided into coarse (more than 25 mm), medium (25-2 mm), fine (2-0.1 mm) and microfine (less than 0.1 mm) particles. Handling coarse, medium and even fine grained gravity concentration equipment, it has large processing capacity, less energy consumption, in the possible conditions are good to use, useful minerals in coarse, medium and even fine grained conditions are selected, which can reduce fine grinding losses and reduce production costs. Dealing with micro-fine grained gravity concentration equipment with poor sorting effect, unless the last resort should not be used. The function of gravity concentration in the production of mineral processing can be summarized as follows.
(1) Ore pre-selection, pre-selecting part of the final tailings under coarse or medium or fine grain conditions to reduce the amount of ore fed into the main separation and reduce production costs.
(2) Main separation of ore, separating useful minerals from veins or enclosing rocks to obtain the final concentrate and final tailings (or medium ore).
(3) Combined process with other beneficiation methods for comprehensive recovery of useful components or separate treatment of coarse and fine grain grades.
(4) Supplementary operation of beneficiation, supplementary recovery of associated components after the main process.
Gravity concentration is increasingly being used not only for sorting traditional mineral materials, but also for the treatment of industrial slags and industrial waste, as well as for the reclaiming of old tailings.
3. Product handling
Handling of gravity concentration products. The dewatering of gravity concentrate is much easier than the dewatering of flotation or finely ground magnetic separation concentrate, because the gravity concentrate contains very little micro-mud. For coarse grain concentrate as long as appropriate drying or drainage filter can be, microfine grain concentrate should also be filtered or dried. The gravity concentration coarse-grained tailings can also be used as building materials or paving stones, while the fine-grained and micro-fine-grained tailings should still be sent to the tailing dam for storage.
2. Gravity concentration diagrams
The process composition of gravity separation is related to the ore yield (vein or sand ore), the particle size of mineral embedding, the value of useful components, the task of sorting operations and the size of production scale. Dealing with cheap iron, manganese ore to try to use a simple process, the coarse separation process of poor sand ore should not be complex. For those high-priced non-ferrous and rare metal ores, in order to reduce the loss of over-crushing, that is, the need to use multi-breaking (grinding) crushing, multi-separation process, but also take into account the scale of production. For those coarse and fine grain products of unequal value (such as diamond, fluorite, etc.) ore, especially to take stage sorting process. Each selection section of the process internal structure (coarse, fine, sweep the number of times, branch circuit, etc.) with the selected ore size, grade and quality requirements of the product. Production is often those with large capacity and sorting accuracy is not high in the equipment arrangement in the coarse, sweeping operations, while the processing capacity of small, high enrichment ratio of equipment set in the selection operations. Due to the nature of the ore variety, so the composition of the gravity concentration process is also a wide range of types, the following is only a simple classification of the composition of the number of sections of the process.
1. Single gravity concentration operation
Refers to the production chain consisting of only a certain gravity concentration process (single or multiple equipment). Ore pre-selection (heavy media selection or jigging), supplementary re-election operations belong to this type of process. The purpose of sorting is only to obtain part of the final tailings or part of the concentrate.
2. Single cycle gravity concentration process
The process contains the system of coarse, fine, sweeping and its preparation operations, such as washing and classification, but does not contain crushing and grinding operations.
This type of process is mainly used to deal with liberated useful minerals of ore, such as river alluvial ore, seaside alluvial ore, etc.. China’s gold mining ship using more trommel screen washing, three stages of jig, a shaking table selection process that belongs to this category (see Figure 1). Treatment of titanium, zirconium seaside alluvial ore for rough concentration by cone concentrator, spiral concentrator selection process also belongs to this category.
3. Single stage gravity diagram
In this process, there is only one section of crushing or grinding operation (such as crushing and grinding is continuous, still should be regarded as one section). This process is often used to deal with residual slope deposit sand ore or iron and manganese ore mined underground. Figure 2 shows the process flow of processing oolitic hematite ore in Longyan Baimiao processing plant, the purpose of sorting is to remove the surrounding rocks mixed in the mining process and restore the geological grade.
4. Two-stage gravity concentration process
This is one of the simplest stages of the separation process. This process is mostly used in small and medium-sized beneficiation plants dealing with wolframite in China, as shown in Figure 3. After pre-selection, the raw ore is crushed by a roller machine, and the product is divided into three grades: coarse, medium and fine, which are treated by jigging and shaking table respectively. The tailings of the first two jigging stages are combined and ground by a rod mill, and then separated by another jigging process, and the tailings are returned to the first cycle, so the process is also called “big closed circuit” process. It can recover part of the tungsten block, but also to avoid excessive complexity of the process. The secondary mud produced in the gravity concentration process and the primary mud from the ore gravity concentration are combined and sent to the mud section for treatment.
The useful minerals in the sludge have almost all been dissociated monomerically, so it adopts more gravity concentration single cycle process, there are fashionable supplemented by magnetic separation and flotation operations. The gravity concentration process in the small and medium-sized plant commonly used are: centrifuge – shaking table – belt chute joint process (see Figure 4); shaking table – swing chute joint process, as well as shaking table – laying chute, hydraulic elimination plate process, etc.
5. Three-stage gravity concentration process
Some large wolframite beneficiation plant, sand tin and part of the vein tin beneficiation plant have large processing capacity of the original ore, in order to adapt to the uneven embedding characteristics of useful minerals, and according to the “fine crushing and coarse grinding, early collection, mud and sand sorting, poor and rich sorting” principle of organizing production, more often used in the three-stage sorting process. In fact, this process is also based on the expansion of the two-stage process. Figure 5 shows the three-stage sorting process of the residual slope sand tin ore processing system at the New Crown Processing Plant of Yunxi Corporation. The process includes two and three stages of grinding (the first stage rod mill is in the ore preparation plant), one, two and three stages of sorting, concentrated rewashing of the secondary concentrate and separate processing operations. The 1.5-0.037mm ore from the ore preparation plant is firstly graded by Φ500mm cyclone and mud separating hopper, and the ore larger than 0.074mm is sent to the first stage shaking table, and the tailing of the first stage shaking table is rod milled to less than 0.3mm and sent to the second stage shaking table for further separation. The rich middle ore (secondary concentrate) of each section is concentrated in the rewash system for two grinding stages and three sorting stages. The ore graded by the incoming ore is graded and deslimed into the fine sand shaking table and the primary ore mud overflow shaker, and the ore mud graded by the coarse grade grinding is put into the secondary ore mud shaking table and the secondary ore mud overflow shaking table. The mud initially removed from the rewash system is fed into the rewash overflow shaking table after de-mud classification.
The primary mud and secondary mud finally removed from the ore separation system are combined and sent to the mud system for treatment. The process is shown in Figure 6 and includes initial enrichment by centrifugal concentrator, belt chute and shaking table selection and fine mud gravity concentration operation. Due to the enhanced hydrocyclone classification and desliming, and the centrifuge instead of the five automatic chute, thus the sorting index has been greatly improved.