Beneficiation of Raw Materials Questions and Answers

Answer: A

Both are true and the reason gives the economics: capacity costs money in every stage, so removing waste while it is still cheap to do so is what makes the whole flowsheet affordable. The principle applies to almost every mineral processing plant.

Answer: B

A reducing agent converts insoluble ferric compounds to soluble ferrous ones that can be washed out. The gain in brightness is modest but often decisive for a paper-coating or fine whiteware grade. A point or two of brightness can decide which market a clay reaches.

Answer: C

Reduction converts the iron to a soluble form that leaves with the wash water, so the iron is genuinely removed rather than merely decolourised. The improvement is permanent and survives firing. Merely masking the colour would not survive the kiln.

Answer: D

Eighty-seven less eighty-two is five points on the scale. Brightness is quoted in points rather than percentages, and a gain of five is commercially significant. Grades are sold against brightness bands only a few points wide.

Answer: A

A slurry is mostly water, and the customer is paying freight on all of it. Filter pressing and drying bring the moisture down to a level at which the material can be handled and shipped economically. Some clay is nevertheless shipped as slurry where the distance is short.

Answer: B

Correct answer: forcing water through a cloth under pressure

A filter press pumps the slurry into chambers lined with filter cloth and forces the water through under pressure, leaving a cake of solids behind. It is mechanical dewatering, removing water without evaporating it, which is why it precedes any thermal drying - as the sequence item in this topic states and the cost item explains.

Answer: C

Both are true and the reason gives the economics: the latent heat of evaporation is large, so every litre squeezed out mechanically saves several megajoules that would otherwise have to be supplied. Every press stroke saves fuel that the dryer would have burnt.

Answer: D

Five hundred multiplied by 2.3 gives 1,150 megajoules, less the small energy the press itself consumes. Figures of this order are why filter pressing is universal in the clay industry. The press itself uses a small fraction of that energy.

Answer: A

Correct answer: False

Thermal drying is far the more expensive, since evaporating water takes about 2.3 megajoules per kilogram while pressing it out takes a small fraction of that. The operations are therefore arranged so that mechanical dewatering removes as much water as it can and the dryer removes only what remains. Sending a wetter cake to the dryer is one of the more expensive mistakes available in a clay plant.

Answer: B

A blunger agitates the raw material with water so that the clay disperses and the coarse impurities can be separated. It is the first wet operation in most clay preparation sequences. Dispersants are often added at the blunger to help the clay break down.