Interaction of Mining Contaminants on the Value Recovery in the Mill

摘要

Negative interactions of mining contaminants, oxidation of ore stocks and loss of values in the mining process, on the downstream mineral beneficiation processes have rarely been publicly documented. Only a few such cases of contamination of cement used in underground backfill operations on the flotation recovery of some base metals have been reported in the literature. Certain mining methods (e.g. Cut-and-fill) result in the contamination of run-of-mine ore with shotcrete. Preliminary experimentation performed by Falconbridge Limited revealed that underground contamination of ore by shotcrete (e.g. as little as 1% by weight) has interacted with subsequent milling process and has led to lower nickel recoveries in flotation. Laboratory testing from the present research project (conducted at Laurentian University), showed that the age of the shotcrete was a factor in its effect on nickel recoveries. Younger aged shotcrete gave nickel recoveries lower than baseline nickel recoveries with no contamination. The initial pH in the flotation pulp was designed to be pH 9.2, but with the young shotcrete contamination the pH was in the neighbourhood of 10.5. Acid addition, used to lower the pH to the optimal operational value, raised nickel recoveries closer to the baseline. The application of sodium carbonate instead of lime as a pH modifier was also another means of bringing the nickel recoveries back to the baseline values. Nickel recoveries plotted at a 4% grade showed that the selectivity of the nickel was much better with the shotcrete contamination, but the overall final nickel recovery was low with the younger shotcrete. Data from the experimental work were statistically analyzed using Student T-tests.