Water-sludge facilities

WATER-SLUDGE FACILITIES (EN: water slurry circuit; DE: Wassersch lammwirtschaft; FR: circuit des eaux schlammeuses; ES: servicio de las aguas y lodos circuito; RU: водно-шламовое хозяйство) is the technological complex for the water supply, processing of the waste and recycled waters, and also of the sludges and tiny wastes (tailings) from the beneficiation. The water-sludge facilities work at the beneficiation plants, which are using the wet methods for the beneficiation.

At the installations of the water-sludge facilities, there are achieved the clarification and purification of the waters, the concentration, dewatering, and storage of the sludges and wastes from the beneficiation, the extraction of the valuable components from the sludges. At the industrial plants, which are beneficiating the coals for the coking, they distinguish three major types of the schemes for the water-sludge facilities: one-stage, two-stage, and combined. The one-stage scheme is used for the industrial plants, which are consuming at most 2 cubic metres of the water per 1 tonne of the coal, which is being beneficiated; the sludge water, after the removal of the particles of the coal with the sizes of more than 0.5 millimetres from this water, arrives to the flotation without the preliminary concentration.

In case of the two-stage schemes, all the sludge water, after the classification of the solid phase, arrives into the concentrator; the concentrated product is delivered to the flotation, and the liquid from the concentrator is returned into the technological cycle of the gravitational separation. The disadvantages of this scheme are associated with the placement of the apparatuses for the clarification of the circulating water on the significant area, but there is not ensured the sufficient degree of the purification, because the usage of the flocculants for the acceleration of the clarification spoils the technology of the subsequent flotation. There are most promising the combined schemes, within which there is concentrated before the flotation only the portion of the sludge water, which is allowing us to ensure the optimal density of the slurry. Within all the technological schemes, the flotation is the obligatory segment of the water-sludge facilities. The concentrate from the flotation is dewatered, the slurry of the wastes from the flotation is concentrated, the wastes are compacted or dewatered, the clarified water is returned into the technological process, or is discharged into the external water bodies, as a rule, after the preliminary purification. According to the identical scheme, there are processed the sludge waters of the industrial plants, which are beneficiating the energetical coals, with the immediate usage of the non-beneficiated dewatered sludge as the energetical fuel.

At the industrial plants, which are beneficiating the coal, the ores of the ferrous and non-ferrous metals, and also the mining-chemical raw materials, using the wet magnetic beneficiation or flotational beneficiation, the water-sludge facilities include also the systems for the water recycling. The average consumption of the water per 1 tonne of the mining mass, which is beneficiated, is 3-4 cubic metres for the coal and petroleum shales (including the recycled water), 6-14 cubic metres for the iron ore, depending on the methods, which are used for the beneficiation, and 5 cubic metres for the apatite ore. The concentration of the wastes from the beneficiation, or of the non-beneficiated sludges, is performed to the maximal concentration of the slurry, for which there is possible the hydraulic transportation of this slurry into the facilities for the storage of the tailings (the settling tanks for the sludge, and the silt accumulators).

At the coal beneficiation plants, the sludges and wastes from the beneficiation are most often directed into the external sectional settling tanks. Upon the filling of the next section, the sediment is compacted during the long time, and, after the reaching of the humidity of at most 45%, is removed using the grapple for the further storage or usage. They clarify the waste liquid from the settling tanks within the silt accumulators. The waste liquid from these silt accumulators, and also from the radial concentrators, is returned into the circulation, or, after the purification, is discharged into the superficial water bodies. In the certain cases, they direct the slurry of the tiny wastes from the beneficiation for the storage into the goaf spaces of the underground mines. Sometimes the water-sludge facilities include the simplified scheme, within which they discharge the sludges and wastes from the flotation, which have been concentrated within the radial concentrator, immediately into the silt accumulator (the storage facility for the tailings).

They intensify the processes of the clarification of the water, of the dewatering of the sludges and tiny wastes from the beneficiation, using the additions of the coagulants, of the macromolecular flocculants, and of the surfactants. They usually calculate the storage capacity of the silt accumulators of the coal beneficiation plants for 10 years; at the ore beneficiation plants, the storage facilities for the tailings are calculated for 10-20 years of the continuous work. The area of the single silt accumulator, and of the storage facility for the tailings, especially in case of the absence of the preliminary concentration, reaches 300-500 hectares. At the coal beneficiation plants, the proportion of the fixed assets, which are associated with the operations for the processing of the recycled and sewage waters, including the dewatering of the products from the beneficiation, is 37-55%. The operating expenditures for the water-sludge facilities, and for the operations for the dew atering (mechanical and thermal) are 34-48%. The labour expenditures for the water-sludge facilities, and for the dewatering, amount to 16.5-18% of the total labour expenditures of the beneficiation plants. Without the taking of the classification into account, the labour expenditures for the water-sludge facilities are approximately by 3 times greater, than for the beneficiation.

Within the schemes of the water-sludge facilities, there is specified the prevention of the pollution of the ground waters and surface waters with the wastes from the beneficiation, and the protection of the agricultural lands, which are adjacent to the storage facilities for the tailings, against the swamping and salination. There is regulated by the special rules within the USSR the content of the mineral salts, of the flotation reagents and flocculants, of the heavy metals, of the cyanides, and of other admixtures within the waste waters of the beneficiation plants, which are discharged into the water bodies. For the prevention of the filtering (it reaches 50%), they use the drainage, and the water-impermeable isolation for the bed of the storage facilities for the tailings. There is specified the final dewatering of the concentrated tiny wastes from the beneficiation within the limits of the beneficiation plant with the help of the settling centrifuges, of the disc and ribbon filters, of the chambered filtering presses, and of the concentrators with the compactors for the sediments. In this case, there disappears the necessity for the external settling tanks and silt accumulators, and the dewatered tiny wastes from the beneficiation are transported into the dumps of the waste rocks.

There are widely used the schemes for the water-sludge facilities with the closed entire-enterprise or local cycles for the recycled water supply. Besides the great environmental protection qualities, these schemes are distinguished with the insignificant consumption of the fresh water, and with the relatively small consumption of the flotation reagents.