Selective flocculation — perspective technology of the enrichment of fine-dispersed coal
The growth of the level of mechanization of coal production and its further treatment leads to the growth of small group part and mineral contaminants in composites produced. Nowadays the coal slacks treatment is one of the main coal enriching problems which is caused by use of traditional technologies incapable to promote necessary rates of substance segregation. The matter is that preparation of fine fraction is characterized with low selectivity and this is the exactly factor that influence the range of coal preparation efficiency. This fact is the main one that define the growing efficiency of fine and small fraction coal preparation in the whole.
Today the main part of slimes is to be treated through the foam flotation [4]. But this process has low efficiency in case of high fine fraction with size less than 50 mkm content in the initial intake. It leads towards contamination of concentrate as well as waste. The alternative process of coal slime flocculation-flotation preparation presupposes a prior treatment of intake flotation with latex flocculants. This process is more efficient and less wasteful comparing to existing technologies of slime treatment. Nevertheless nowadays all the activities in the field of the coal selective flocculation with synthetic latex need to be improved and fuller theoretical explanation of some stages of the process. That is why a further elaboration of the selective fine coal flocculation process with synthetic latex theory and the process technique improvement on this basement are necessary. Therefore they become an urgent theoretical and practical issue.
The purpose of work is improvement of quality of coal of fine–dispersed material with the help of the technological scheme enrichment technology of selective flocculation. Work will also revealed and proven to both theory and practical advantages of enrichment of coal sludge oils.
So, to technologies that belong technology called «selective flocculation», which in comparison with the existing technologies of processing of sludge is more efficient and cost–effective.
Selective flocculation — a set of processes selective aggregation of fine particles of mineral resources in micro floccules size 100–300 microns using reagents–flocculants of a different nature. Last, as a rule, are entered in water dispersion of fine-dispersed material, which are subject to intensive campaigning in the turbulent regime mixing of the slurry. In turbulent flows suspension is selective fastening units on the surface of particles of a certain nature with their subsequent binding due to the flocculent in spatial structures - micro floccules. At this crucial relationship flocculent and the surface of the particles. Department flocculation product of dispersed particles can be carried out by gravity, flotation and magnetic method. Selective flocculation is a universal process and can be applied for various kinds of mineral resources: ores of ferrous metals (especially, manganese), oxides and sulphides of non–ferrous metals, sludge of rare metals, gold sand, sludge of non-metallic raw materials. Depending on the type of the applied reagent can be divided into four basic types of processes of selective flocculation of coal — inorganic electrolytes, oils, water–soluble and hydrophobic polymer compounds. Type of reagent has a decisive influence on the results of the process, since the mechanism an aggregate appears. Take a closer look at selective flocculation coal sludge oils.
Of great interest are a variety of technologies of selective flocculation using as flocculants oils. As already noted, the high costs linking and duration of the turbulent mixing in the processes of oil granulation are dictated by the necessity of obtaining granulated product for a specific size (1,5–2 mm), which ensures its efficient allocation with mineralized suspension on stationary screens. If you refuse to get big and strong granules, at the presence of a sufficiently effective method of fine aggregates (focal), conditions are being created for a sharp reduction of duration of the process, as well as costs of the reagent. It is followed this way the authors, offering a new type of process of selective flocculation ОВЗУМС — «enrichment of highly zol'nys coal oil selection». The essence of the method consists in the high–speed aggregation of coal particles in micro floccules (0.2–0.3 mm) for 0.5–3 minutes of turbulent mixing water-coal suspension with oil by a reagent. Department flocculation product may be either due to air effect in the flute machines, or in the centrifugal field of settling centrifuges. Perhaps a combination of oil breeding with subsequent granulation flocculation product at the expense of additional portions of oil binder in the amount of 10–15% of the mass of a solid. Technology is low–cost units-oil (0,5–2%) and high selectivity of separation. The range of its applicability — enrichment and dehydration of coal, mainly of highly zol'nys (up to 50–70%), fine (50–70 m and less) coal slurry from suspensions of small density (1–10 masses.% solids), which belong to the heavily enriching.
Analogues process ОВЗУМС developed in a number of research centers of Germany, great Britain, the USA, Canada, Japan and other countries. Some varieties processes «Konvertol», «Oliflok»,the NRCC have a relatively small expenses binder (up to 5%) and in their characteristics may be considered as prototypes selective oil flocculation. For the first time selective oil flocculation used as subproces in the indian variant technology, called "pancake week agglomeration" (MA). This technology was developed in the 1970s in the Central research institute of fuels India (Central Fuel Research Institute, D.Sarkar, Bkhattachach'ya and etc.) .
This technology option was implemented by «Bharat Kouking Cole co., LTD.» (Lodna, India) on semi industrial installation with the capacity of 2 t/h (fig.1). The first coal sent on wet grinding and the pancake week flocculation in the layer mill and (or) the vat. Suspension of flokulation coal–and–water, injected highly viscid oil and the obtained mixture is consistently stirred in the two horizontal at pv1=400 min-1 and пв2=600 min-1. The agglomerate dehydrated on the arc of the city, and then on vibrant crash. Agglomerate subjected to the formation of lumps with a binder on granulator dry type. The source material — a coal grain size of 0,1 mm, and coal slimes of 0–0,5 mm. Expenses low-boiling (diesel) oil on the stage of the oil flocculation were 1–2 masses.%, high boiling point (creosote, furnace oil) at the stage of agglomeration — 10–18 masses.%. The environment, meadow, in suspension at the stage of flocculation was measured out. After dilution with water concentration suspensions decreased with 35–40% to 15–20%. Duration of agglomeration –3–8 minutes. When the ash output Ad =17–41% products characteristics agglomerations of were such: ash sinter Ad =9–22%;the value of the dа=2–8 mm; humidity W =10%; the ash content of waste oil agglomeration Аd =62–71% In the second variant technology (fig.2) the source coal of subjected to selective oil flocculation in colloid mill during 1–2 min., then the suspension was diluted with water, injected highly viscid binder and performed agglomeration in flute chamber without the flow of air. The agglomerate dehydrated over the arc sieves and vibrant crashes of or on the arc sieves and in the mixture with coal grain size 0.5 mm — on the filtering centrifuges a matter of fact the Indian version of the technology are one of the first striking examples of implementation of the oil flocculation fine coal, although it is used as a part of the process of selective oil aggregation.
Oil flotation — the process of selective flocculation of coal with subsequent flotation units. Method is intended for enrichment and dehydration of coal size 0–1 mm. According to him water–coal pulp density of 35–40 % of the solid phase class 0–0,5(1 mm) is mixed with and mixture of paraffin and tares oil in the proportions in accordance 1–1,5 wt.% + 0.05 and 0.2 wt.% of the dry coal. Pulp with reagents is mixed in the turbulent regime, coal of oils flocculent removed flotation without adding additional reagents and then dehydrated into centrifuges.
The Process of "Aglofloat" provides selective flocculation or agglomeration of fine-dispersed material with the subsequent removal flocculent (to the agglomerate) flotation. Developed in the late 90-ies he was tested for cleaning oil for soil, as well as for the desulphurization of coal. In the latter case the processing of coal is the grain size 0–0.6 mm. Expenses of the oil reagent is 0,5 — 5 wt.% of the dry coal. Duration of campaigning pulp 30-60 with. The concentration of the pulp — 10 % of the solid phase.
Test process on sub bituminous coal mines Montana shows that with the use of mixture of bitumen and heavy oil (Qм = 5 wt.%) the process of «Aglofloat» provides reduction of the sculpture content in coal from 4.4 % to 1.8 %. At the same time removes about 95 % inorganic (pyrites) of sulfur.
Selective flocculation oils successfully combines the advantages of both oil granulations (high selectivity of separation, the possibility of fine–dispersed fractions with particle size of less than 40–50 m), and froth flotation (emphasis concentrate due to air effect). Due to this it in and by number of cases can compete effectively with flotation and with the «classic» oil granulation moreover, in the case of processing in high-ash bituminous coal from suspensions low density it is the only effective way of dressing.
