| Summary: | 碩士 === 大葉大學 === 環境工程學系碩士班 === 98 === The main purpose of this study is to recover the gold, silver and copper form plasma molten slag. The scopes of this study of project include：Component analysis of plasma molten slag; Study on the screening of plasma molten slag; Study on the magnetic separation of ferrous and non-ferrous material; study on treatment processes for recovering and purifying the precious metals such as leaching, ion-exchange, precipitation, replacement, electric wining, andcrystallization.The results of this study reveal that 90.6% of copper can be leached from the crushed powder of the plasma molten slag of size less than 0.149mm by using 18N H2SO4 at solid/liquid ratio=10g/50mL and 70 ℃ for 1 hour of leaching operation. About 58% of copper contained in this leachate can be crystallized as CuSO4．5H2O after standing for 48 hours at 27 ℃. The copper still remained in the solution can be completely recovered by using iron powder replacement. Subsequently, the second leaching treatment was performed on the residue by using 18N H2SO4 at solid/liquid ratio=10g/50mL and 70℃ for 2 hours. Also, 100% of copper contained in the second leachate can be recovered by iron powder replacement.
The silver contained in the second residue can be completely leached out by using 8N HNO3 at solid/liquid ratio=1g/50mL and 70℃ for 2 hours of leaching operation. The silver can be 100% precipitated by adding HCl to the solution in which the pH was previously adjusted to 10 by adding NH4OH. 100% recovery of gold from the residue can be obtained under optimum leaching condition by using 100% aqua regia at solid/liquid ratio=0.5g/50mL and 70℃ for 4 hours. All of gold contained in the leachate can be recovered by using zinc powder replacement.
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