Define Double Refractory Ores as associated with gold deposits and how they affect the mineral recovery in...

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Mechanical Engineering

Define Double Refractory Ores as associated with gold depositsand how they
affect the mineral recovery in extractive metallurgy.

ii. Briefly explain Pregrobbing and propose three ways ofreducing pregrobbing in
gold metal recovery.
b.
i. State and explain briefly five (5) types of mills anddescribe their grindings

3.
ii. Describe the motion of a charge in a tumbling mill

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Define Double Refractory Ores as associated with gold deposits and how they affect the mineral recovery in extractive metallurgy AnsA double refractory gold ore usually contains both sulfide minerals and carbonaceous matter and results in very low gold extraction The microsized gold particles are enclosed inside the mineral lattice and cannot be extracted even with very fine grinding The carbonaceous matter pregrobs gold leading to loss of gold values to the residue Thus pretreatment is required to decompose the sulfide minerals and carbonaceous matter prior to cyanidation The conventional process involves roasting the ores at 450C 700C or to pressure oxidize the ores in an autoclave at 180C 200C To avoid the elevated temperature operation the microbial pretreatment process was used in this investigation Three kinds of micro species were used in this study The chemolithotrophic bacteria Acidithiobacillus ferrooxidans Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans were used to decompose the sulfide minerals and expose the gold particles to the lixiviants The actinomycete Streptomyses setonii decomposed the carbonaceous matter and eliminated the pregrobbing problem The white rot fungus Trametes versicolor indirectly decomposed the sulfide minerals and passivated the carbonaceous matter The pretreatment could be conducted in two stages with the combination of the micro species or with one micro species Three different ore samples were used for the test works and the results demonstrated that over 85 94 of the gold could be extracted by cyanidation after microbial pretreatment ii Briefly explain Pregrobbing and propose three ways of reducing pregrobbing See Answer

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