Abstract
Large areas of storage sludge pose a risk of contamination of soil, groundwater and crops, respectively, pose a significant risk to humans and other living organisms, because heavy metals accumulated in plants are included in food chains and enter the gastrointestinal tract with foodstuffs. Over time, sludge stores overflow, causing the need to build new structures. The introduction of sludge recycling technologies will free up the area occupied by sludge storage facilities, eliminate the cost of building new sludge and profit from the extraction of valuable components. Such, for example, is zinc, whose content in natural raw materials is 1-3 %, and in the waste of the production of viscose fiber 6.5-40 % (depending on the range of products, and reagents used for wastewater treatment). Zinccontaining sludge at medium-sized enterprises is 1,000,000 tons, allowing it to process that amount of sludge with a capacity of 10 tons per hour for 10 to 15 years. In the early works in the laboratory, physical and chemical laws of zinc-containing sludge processing were established and technological process of sludge utilization into zinc sulfate was developed, the composition and physical and chemical properties of zinc-containing sludge were investi-gated, the conditions of processing and rational ways of utilization were determined, the influence of temperature on contact duration, reagent concentration, mixing intensity was investigated for the zinc hydroxide extraction process, zinc content purification technology was proposed, impurity solution, comparative feasibility studies and cost effectiveness of sludge processing were performed. The paper presents a study of hydrometallurgical method of processing zinc-containing sewage sludge by leaching. The removal of zinc from the sludge is carried out on a semi-industrial installation. To study the particle size distribution of the source ore, wet sieving method is chosen. Phase chemical analysis on the forms of zinc is carried out. Also, X-ray and thermogravimetric analyzes are applied to study the real composition of the sample. On the basis of a series of experiments on a semi-industrial installation, the main stages of technological process are identified and investigated. According to the results of the research, the technological process of obtaining zinc sulfate from zinccontaining sludge production of viscose fiber is developed. It is proposed to divide the process into separate stages, in order to develop a flexible technological scheme, which allows the processing of different raw materials. For complete and effective extraction of zinc, the insoluble residue after the leaching step is proposed to be treated with a nitric acid solution, which allows to obtain an additional product – calcium nitrate enriched with micro-impurities. According to preliminary ecological and economic calculations, the profit from the sludge processing for one year will be about EUR 1.684 million. Through the implementation of the proposed scheme for the use of secondary products, a significant social effect is achieved by improving the environmental situation by reducing the amount of waste in the sludge collectors, creating jobs.
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