Immobilization of arsenic from copper smelter waste
Kemian tekniikan korkeakoulu | Master's thesis
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Minerals and Environmental Engineering
Erasmus Mundus Minerals and Environmental Programme
AbstractArsenic is an inconvenient impurity for copper smelters and its problematic its bound to worsen as concentrates become dirtier. Air emissions are prevented during the off-gas treatment so it deports to liquid effluents and dusts. From effluents it cannot be removed easily together with other metals and specific removal needs to be considered. At industrial level the preferred choice is precipitation and copper smelters thus seek precipitates that are safe enough for inexpensive landfill disposal. The literature review identified the most common methods used by industry as well as more novel proposals to remove arsenic from solution. When precipitates or other types of solids are still too hazardous for safe disposal, it is possible to stabilise them with other methods discussed. The experimental work tested one solid stabilisation approach, vitrification, on hazardous copper smelter waste. Next, after producing an arsenic bearing solution similar to copper smelter effluents by leaching the same waste, five precipitation methods were tested: high iron arsenical ferrihydrite, a two-step process using aluminium and iron, arsenate hydroxyapatite, gypsum seeded scorodite and ferrous arsenate (symplesite). The short term leaching behaviour of the solids was tested with 24 hour bottle tests performed at different pH conditions. The results showed that all methods produced solids somewhat safer than the original one, but only the symplesite and two step precipitation methods have resulted in solids safe enough for landfill disposal. A preliminary cost estimation shows that these methods could be competitive with existing processes, while producing a safer solid. Regarding vitrification of the current waste, even though the particular conditions of the test were unable to produce a safe enough solid, the waste proved amenable to the process.
Thesis advisorGullón Corral, Lidia
arsenic removal, arsenic precipitation, immobilization, copper smelter waste, vitrification