The inner and outer surfaces of concrete lining in deep alluvium freezing shaft are exposed to different temperatures, taking the hydration heat of cement for pyrogen. Additional stresses are therefore observed in concrete lining, owing to its marked temperature drop at early ages. This paper makes a numerical calculation of the temperature and the thermal stress on freezing shaft lining by finite element methods and engineering monitoring. The results reveal that the concrete of shaft lining has a high heat-release rate in the early age. And the time when shaft lining reaches its maximum temperature is 4 days earlier than it reaches its maximum thermal tension stresses. At the time of one day after the shaft lining pouring, the inner and outer surface of shaft lining will crack owing to its hoop tension strain is greater than ultimate tension strain. The crack of concrete will increase with the modifications of temperature.
Redissolution of cemented cobalt from zinc sulphate solution occurs, and is a well known problem among zinc producers. A variety of mechanism of cobalt redisisolution have been proposed in the literatures, however, it is still not very well understood. The influencing factors of cobalt redissolution such as detention time, oxidation, particle size of zinc dust and copper ion have been investigated in this paper. The redissolution does not occur when very large particles are used but the redissolution of cobalt is significant from small zinc particles. The redissolution is obvious with copper ion added, while the redissolution is not occurred from the zinc sulphated solution without copper ion added. The redissolution mechanism of cobalt is obtained.
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