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Tutorial $4$

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$6.$ You are appointed as a junior metallurgist in the Anglo$-$American plant dealing with the recovery of PGMs in the Bushveld igneous complex. After their prospective survey, the plant geologists confirmed that the plant would be dealing with a seam of mixed sulfide and oxide ores. It should be noted that from their survey, all the PGMs are trapped in the sulphide matrix made of Chalcopyrite, pyrrhotite, and pentlandite, and the seam has the high grade of $Cu$ and $Ni.$ Therefore, there is no need for concentration. You are selected as a team leader to coordinate and proposed a clear chain value route to recover PGMs and principal elements such as $Cu$ and $Ni$ as the by$-$products using the hydrometallurgical route. After the study, you and your team proposed four scenarios to recover $Cu$ and $Ni.$

The first consists of Roasting $-$ Leaching $($acid$)-$ Clarification $($Fe removal$)$ Purification $($solvent extraction: LIX $63$ and LIX $64)-$ Metal recovery $($electrowinning$)$

The second consists of Direct leaching $($acid or base: please define conditions$)-$ Clarification $($Fe removal$)-$ Purification $($activated carbon$)-$ Metal recovery $($cementation and precipitation$)$

The third consists of Melting $-$ Reduction $-$ leaching $($acid$)-$ Purification $($activated carbon$)-$ Metal recovery $($cementation and precipitation$)$

The fourth consist of Melting $-$ reduction $-$ Metal recovery $($electrorefining of copper only$)$

$($a$)$ Propose a detailed flowsheet of the given scenario and explain the processing route to extract base metals with the support of chemical reactions at each stage. Along with the presentation, justify the choice of the leaching agents since it is very crucial. Moreover, the choice of the leaching agent must address at the same time the technical aspect $($equipment lifetime$),$ the environment $($management of gases and effluent$),$ and economic aspects $($recycling$).$ The flowsheet should be extended to the recovery of PGMs $($on the precious metal route stop the generation of pregnant solution$).$

$($b$)$ Considering that the pregnant solution from the base metal refinery section contains $100$ ppm of $Fe,$ which must be discarded at clarification in the form of $Fe(OH{)}_3,$ at which $pH$ the Fe will start precipitating if the $Ksp$ is $Ksp=6*{10}^{-38}.$

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