English to Arabic Tech/Engineering Mining & Minerals / Gems Mineral deposits (phosphate)

The phosphate grade is quite low at 14% P2O5 (where the commercially mined deposits tend to have between 29,7% and 39,1% P2O5), but it has been shown that grades can be improved to 34% with the removal of clay slimes.

From the hits I got on the net it seems that this is a fixed expression in the mining industry.
I hope that there is an expert out there who can help.