Raw Materials and Quarrying Questions and Answers

Answer: A

Correct answer: about one four-hundredth

A reclaimer cutting across all the layers takes a slice of each with every pass, so any single layer contributes about \( 1/400 \) of the material reclaimed at any moment. That is the whole purpose of layered stockpiling: a variation that arrives over hours in the incoming stone is spread across the entire pile and reaches the mill diluted several hundredfold.

Answer: B

Correct answer: must be evaporated, which consumes fuel and kiln capacity

Every kilogram of water in the feed must be boiled off before anything else can happen, at about 2.3 megajoules per kilogram, and the vapour then occupies gas handling capacity. In a dry process plant that heat comes from the kiln exhaust, so wet raw materials reduce the throughput as well as raising the fuel per tonne - which is why moisture is monitored and stockpiles are often covered.

Answer: C

The wet process feeds a slurry containing a great deal of water, all of which must be evaporated in the kiln at considerable cost. This is the main reason the dry process with preheaters has replaced it almost everywhere new plant has been built.

Answer: D

Where chalk and clay come out of the ground wet, the cost of drying them may outweigh the saving from a dry kiln, and slurry blends very easily. The advantage is one of the particular deposit rather than of the process in general.

Answer: A

Where a deposit varies, benches of differing composition can be worked in proportion to give a consistent blend. It is a cheaper way of controlling chemistry than buying corrective materials, and it extends the useful life of a variable deposit.

Answer: B

Both are true and the reason gives the advantage: material that would be waste on its own becomes usable when blended, which both extends the reserves and reduces the quantity of corrective material that has to be bought in.

Answer: C

The first is 2 above the target and the second 6 below, so they must be mixed in inverse proportion, three to one. This is the mixing rule used constantly in raw mix control and is worth being able to apply quickly. The rule works for any two components blended to a target between their values.

Answer: D

Correct answer: 4,000 tonnes

\[ \frac{1{,}200{,}000}{300} = 4000\ \mathrm{tonnes\ per\ day}. \] The quarry works fewer days than the kiln, which runs continuously, so the quarry’s daily rate must exceed the kiln’s consumption and the difference is held in the stockpile - which is one of the reasons the stockpile exists at all, alongside the blending function.

Answer: A

A cement works represents an investment lasting decades, so a deposit is normally proved to supply it for thirty years or more before the plant is built. Reserves and plant capacity are settled together rather than one after the other.

Answer: B

The capital cost is so large that thirty years or more of proved reserves is the usual requirement before a decision is taken. Building beside a short-lived deposit would leave a very expensive plant stranded without feed.