I know of no reason why you should not use phosphogypsum. However, you will have to conduct trials to verify that no product quality problems are involved.

How does the content of chromium have influence in quality and performance of grinding balls? Is it better a low content of this metal to improve hardness in balls?

If the grinding balls contain chromium then they are forged, hard grinding balls. If the balls don't contain chrome then they are softer mild steel and the wear rate will be higher. Balls containing chrome cost more but last significantly longer and maintenance of the optimum media loading in the mill is easier. Many cement companies use soft media for raw grinding as the wear on the steel simply increases the iron content of the raw mix slightly. Most cement companies use hard media for cement grinding as the wear rate on soft media when grinding clinker is too high and the mills need continuous recharging.

Our facility operates two Humboldt air-swept ball mills for raw meal production. Combined capacity is 100tph. We would like to optimise the raw meal circuit, in particular, mill loading. Unfortunately, there appears to be very little information on the optimisation of air-swept mills. How can mill throughput be improved, utilising existing equipment? The separator is a mechanical classifier, with adjustable vanes. Current reside set point is 15 per cent on 90 micron. We currently use sonic ears to determine mill loading, with mill and fan current also available. There is also a proposal to implement a grit return weigh system to determine the recirculating load. Would this be worthwhile addition, with any positive process benefits? In summary, we wish to determine the most cost effective means of attaining optimal material levels in the milling circuit, with the intention of automating the operation sometime in the future.