Beneficiation of Raw Materials Questions and Answers

Answer: A

Separation raises the proportion of the wanted mineral without changing its chemistry, which is a different operation from grinding or blending. A deposit that would otherwise be unusable can often be brought within specification this way.

Answer: B

High-pressure water frees the kaolinite and carries it away while the coarse quartz and mica settle out. The fine fraction is then classified further to reach the particle size the market wants. Paper-coating grades are far finer than ceramic grades.

Answer: C

Both are true and the reason gives the arithmetic: several tonnes of rock are handled for each tonne of clay recovered, which is why the waste tips of a clay district are so conspicuous a feature. Cornwall's white tips are the visible record of that ratio.

Answer: D

One in eight is one eighth, or 12.5 per cent. Recovery figures of this order govern both the economics of a deposit and the quantity of waste that has to be disposed of. Waste handling is a major part of the cost of clay production.

Answer: A

Coarse and dense particles settle faster and are removed, leaving the fines in suspension. It is the same principle as sedimentation size analysis applied at production scale rather than in a laboratory. Hydrocyclones do the same job continuously and at much higher throughput.

Answer: B

Correct answer: False

Hydraulic classification separates by settling velocity, and that depends on density as well as on size - Stokes’s law contains the difference between the particle and fluid densities. A small dense grain therefore settles with a large light one, and the two report together. That is a limitation when the impurity is dense, and it is exactly what makes a classifier useful when the impurity is both coarse and dense, as quartz is in a clay.

Answer: C

Both are true and the reason gives the basis: the same dependence that complicates size analysis is what makes gravity concentration possible, so the effect is a tool rather than merely an error. The same physics serves two quite different purposes.

Answer: D

Even a small quantity of iron produces a marked discolouration in a body intended to fire white. High gradient separators can remove weakly magnetic minerals that an ordinary magnet would leave behind. Brightness specifications for paper-grade kaolin are extremely demanding.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the necessity. The iron and titanium minerals discolouring china clay are weakly paramagnetic, not ferromagnetic, so an ordinary separator exerts too little force on them. A high gradient machine fills the gap with a fine ferromagnetic matrix, which concentrates the field into very steep local gradients and captures particles a conventional magnet would pass straight through.

Answer: B

Correct answer: False

Magnetic separation covers a wide range of susceptibilities. Strongly magnetic minerals such as magnetite are removed by a simple drum magnet; weakly paramagnetic ones such as hematite, ilmenite, biotite and iron-stained anatase need a high intensity or high gradient machine. Whether a mineral can be separated depends on the equipment as much as on the mineral, which is precisely the point of the previous item.