Use of Waste Phenolic Water from Coke-Chemical Plants in the Flotation of Coal Slimes
Abstract Generated abstract
This paper examines the possibility of using phenol-containing wastewater from coke-chemical and related gas plants as process water in the flotation of fine coal slimes, combining wastewater dephenolization with coal beneficiation. The authors argue that, after preliminary phenol removal, final purification can be integrated into flotation because coal has sorptive capacity and phenolic impurities may act as frothing agents. Laboratory tests on 1 to 0 mm coal slime using wastewater containing 300 mg/l phenol showed a higher concentrate yield than distilled water without frother, with similar ash content, and a control experiment indicated that 77% of phenols entered the froth product. The study suggests that this approach may reduce reagent consumption, intensify flotation, and contribute to wastewater treatment at coke-chemical facilities.
Full Text
USE OF WASTE PHENOLIC WATER FROM COKE-CHEMICAL PLANTS IN THE FLOTATION OF COAL SLIMES
L. F. PROSEKOVA, S. A. BABENKO, V. M. VITYUGIN
(Presented at the scientific final conference of the Faculty of Chemical Technology)
The quality and quantity of wastewater from coke-chemical plants depend on many factors: the quality of the coal being processed, the technological processing regime, the design of the gas-cleaning installation, and the state of the enterprise’s water-management system. The effluents of coke-chemical plants contain a number of impurities that are highly harmful to bodies of water. The most widespread and harmful among them are phenols and tar. Therefore, before these waters are discharged into a body of water, they must be subjected to purification.
An analysis of the technological essence of all known methods, both in the USSR and abroad, for rendering wastewater harmless shows that there can be no universal general method for solving the problem of purifying the wastewater of industrial enterprises. For each type of wastewater, a special method for rendering it harmless must be developed, taking into account the specific characteristics of the given waters. The same analysis of known methods for treating wastewater leads to the conclusion that complete and effective results in rendering wastewater harmless can be achieved by applying multistage treatment of the waters, consisting of two or three successive processes of decontamination.
The first stage of purification should consist in extracting the main mass of phenols for the purpose of their utilization by the sorption method, the extraction method, or by the method of stripping with live steam, followed by absorption of the phenols with alkali.
Such preliminary purification reduces the phenol content in the wastewaters of coke-chemical plants from 2000 to 300 mg/l.
The second stage, the final purification from phenol, could be combined with the process of flotation of fine coal. Fossil coals, owing to their porosity, possess a high sorption capacity. Thus, according to Emel’yanov [1], the sorption capacity of certain hard coals for methane reaches 21.4 cm³/g, which is only four times less than that of such highly active adsorbents as activated carbon. Therefore hard coal may find application for purifying the wastewaters of coke-chemical plants from harmful impurities dissolved in them, including phenols. In practice this is easy to carry out in the process of flotation of coal slimes at coal-preparation plants attached to coke-chemical plants.
The use of wastewater for coal flotation will lead to a reduction in the consumption of flotation reagents, since the substances contained in the wastewaters—
phenols are good frothing agents. The improvement of the flotation of coal slimes will also be promoted by the elevated temperature of the waste water.
The use at coal-preparation plants of pulp heated to 25–30°C increases the productivity of the flotation machine by 15–20% [2].
According to literature data, the amount of waste water from coke-chemical plants per 1 ton of coal charge is up to 2 m³. The effluents from chemical processing of coal and gas purification (containing phenol) amount to approximately 50% of the total quantity of waste water, i.e., up to 1 m³/t. The S:L ratio in flotation pulps is usually 1:4, i.e., 4 m³ of water per 1 ton of coal fines. In the overall balance of the charge for coking, flotation concentrate amounts to 20–25%, or 0.2–0.25 t per 1 t of charge. Consequently, all the waste water can be supplied to flotation.
The possibility and expediency of using, in coal flotation installations, wash water containing residues of coal-tar resin and oils has already been demonstrated. The possibility is also known of using, in the coal-preparation process, heated water from cooling apparatuses and discharge waters from water-treatment facilities [3].
The question of using the discharge waters of the chemical shops of coke-chemical plants for the flotation of coal slimes, with their simultaneous dephenolization, has not been studied. To clarify this question, we carried out preliminary laboratory investigations of the flotation of coal slime of the 1–0 mm size class, obtained from the Chertinskaya CPP, using waste water from the TPI gas plant with an initial phenol content of 300 mg/l. Considering that the temperature regime of coking differs little from that in coal gasification in retorts, the chemical composition of waste water from gasification practically does not differ from the waste waters of coking.
To determine the influence of impurities contained in the waste water on the flotation process, comparative tests of coal beneficiation were carried out using distilled and phenolic water without adding a frothing agent.
The experiments were conducted on a mechanical-type flotation machine, chamber capacity 0.5 l, with an impeller speed of 2000 rpm, S:L = 1:4, pulp temperature 18–20°C; sulfonated kerosene was used as the collector, at a consumption of 1 kg/t.
The tests showed that, if with phenolic water the concentrate yield was 61.3% at a concentrate ash content of 9.44%, then with distilled water without frothing agent the concentrate yield was only 49% at an ash content of 9.01%.
For a preliminary assessment of the degree of purification of the waste water from phenols during flotation, a control experiment was carried out with an analysis of the distribution of phenols among the flotation products; it turned out that 77% of the phenols passed into the froth product.
Thus, the use of waste water for flotation is expedient, since, along with purification of the waste water from phenols, an intensification of the flotation process of coal slimes takes place.
LITERATURE
- D. S. Emel’yanov. Theory and Practice of Coal Flotation. Ugletekhizdat, 1954.
- M. G. El’yashevich, E. I. Pushkarenko. Experience in Coal Flotation. Gosgortekhizdat, 1960.
- P. N. Gorelov, T. I. Gornykh, F. A. Mustafin. Purification of waste waters from oils and resinous substances in a flotation machine. Coke and Chemistry, No. 8, 1961.