The paper deals with the physical properties and chemical composition of rice husk and dust, which are the waste of the Regulus raw rice growing in the Krasnodar Region of the Russian Federation. Rice dust is formed as a result of the discharge upon the receipt of raw rice from vehicles, removal of impurities, sorting by size, during separation of membranes, crushing, grinding, polishing, moving grain along the elevators and conveyors, i.e. during all technological operations production of rice groats. In order to remove dust, the group cyclone and the bag filter-cyclone are installed in the pneumatic conveying systems and suction plants of "Southern Rice Company", LLC. The paper shows the chemical composition of samples of husk, dust retained by the group cyclone, and dust retained by the bag filter-cyclone. Rice husk contains a significant amount of silicon dioxide -14.8%. The dust collected from the group cyclone contains ferrum (109 mg/kg), plumbum (1.1 ± 0.4 mg/kg), and copper (1.2 ± 0.4 mg/kg). The bag filter-cyclone retains finer dust particles. The dust collected in the cyclone is of yellowish-pink color, and the dust, collected from a bag filter-cyclone, is gray. Fine dust, which has passed through the filter, is drier than the dust, segregated in a cyclone, so it is more explosive and easily ignited. Dust can cause the explosion. The dust properties give an indication of the degree of its danger and the ability to form explosive concentrations in air.
Quantitative chemical composition of ash and slag mix generated upon combustion of Donetsk culm is determined. It is established that ash and slag mix of Novocherkassk state district power plant (SDPP) (Rostov region, Russia) after coal combustion has the following composition: iron -2.3%; mineral constituents -75.8%; calcium oxide -20.4%; aluminum oxide -0.0118%; water -1.3022%; manganese oxide -0.18%; copper oxide -0.0043%; plumbum -0.0017%; it is qualified as hazard class IV for environment. Cadmium, mercury, arsenic, selenium, antimony, bismuth are contained in trace amounts < 0.1 mg/kg. In order to reduce dust emissions the cleaning stage I of gas scrubbing facility is equipped with group cyclone comprised of four cyclone units. Medium and coarse particles under the action of centrifugal force are deposited in the cyclone. This promoted decrease in dust load on bag filters, the cleaning stage II. Qualitative chemical composition of ash captured by group cyclone and that of ash captured by bag filter are determined. Cadmium, copper, plumbum, zinc, iron, manganese, and calcium are contained in coarse and fine particles captured by group cyclone and bag filter. Aluminum referred to light metals is completely captured by cyclone. The ash dust in its bulk is of dark gray color. The ash captured by cyclone contains coarse particles of black color and the ash captured bag filter contains fine particles of light colors (gray-yellow color producing silky gloss). This is characteristic for ash dust after combustion of Donetsk culm. The main component of the ash is silicon dioxide, its content in the ash captured by filter reaches 91%. These fine particles create light tone of this ash.
Ash and slag wastes after coal combustion at power plants are usually considered as environmentally non-hazardous. The term "toxic" is not applied to ash and slag. This article discusses the results by researchers of several countries concerning the aspect of determination of hazard class of ash and slag wastes after coal combustion at power plants. Toxicity of ash and slag mixture has been determined experimentally using test organisms, contrary result has been obtained. Biotesting has been performed according to testing procedures (the Russian Federation) specified by the Federal Register, FR 1.39.2007.03222 and FR 1.39.2007.03223. While analyzing toxicity of ash and slag mixture after combustion of culm of Donetsk deposit (Russia), acute toxic impact water extract from waste on test organisms, Daphnia magna Straus and weeds Scenedesmus guadricauda, was revealed. Non-hazardous dilution factor water extract from waste has been detected, causing lethality of not more than 10% of daphnia in 96 h and deviation of quantity of weeds not higher than by 20% in 72 h in comparison with reference. Ash and slag wastes are classified as hazard class III-IV for environment which agrees with the results by other researchers.
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