Browsing by Author "Kivi, Jenni"

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Ruostumattoman teräksen kierrätyksen merkitys ja organisointi Suomessa
(2012-11-29) Kivi, Jenni
Kemiantekniikan korkeakoulu | Bachelor's thesis
Wastewater treatment technologies and water recycling in mining and mineral extraction processes – a literature survey
(2014-02-11) Kivi, Jenni
Kemian tekniikan korkeakoulu | Master's thesis
The aim of this study is to consider the possibilities in reasonable and efficient water usage and high water recycling rate in mining and mineral processing industry. Wastewater treatment technologies for different mineral industry wastewaters are described and the basic chemistry behind the processes explained. The thesis also describes the reasons for water use in mineral extraction processes, the wastes formed in the processing of ore and minerals, the common reagents used in mineral processing and the best available techniques considering mining activities. Water is widely used in mining and minerals industry: for processing and transporting of ore and waste, minerals separation, dust suppression, washing of equipment, smelter refractory cooling systems and human consumption. Both economic and environmental considerations make the recycling and re-use of water an absolute necessity. The industry has made much progress in developing close-circuit approaches that maximize water conservation, and responsible management of water is a key ingredient in ensuring that mining companies’ contribution to sustainable development is positive over the long term. Factors that have led to increasing recycle of the used process water are following: water use of the mineral processing plants may represent a large proportion of the local water resources, the production and transportation of fresh water are usually expensive and the effluents from the processing operations are potentially harmful to the environment. Common characteristic of mineral processing water is the presence of ions and chemical compounds with a high pollution potential. One of the most satisfactory ways of dealing with this problem is the total recycling of reject waters, but several technical aspects influence the extent to which recycling can be performed. The chemistry of the system could affect the process efficiency, which applies especially to flotation which is principally governed by the chemistry of the ore. There is a specific ionic composition in every process section at which the process can conveniently be operated. Circulating the water in the process could result in cost-savings if the water was purified only to an acceptable level concerning the process and not to a level that is needed when water is discharged back to local water bodies. Thus, the amount of process water needed from the outside of the production plant is also decreased. Recycling in gravity and magnetic concentration circuits creates no problems. Recycling in simple flotation circuits with a monometallic or bulk concentrate is also well developed. Multi-stage circuits using selective flotation face the most serious problems in recycling. In the cyanide gold industry, recycling is limited due to the build-up of complex chemical compounds and a high concentration of sulfates. In the uranium plants using acid leaching, recycling is not practiced because of the impurities and incompatibility with the process – alkaline leach solutions, instead, are recycled. Mine water is recycled in the grinding-thickening circuit.