Industrial use of nitrogen in flotation of molybdenite at the Sarcheshmeh copper complex

The Sarcheshmeh copper deposit contains 1 billion tonnes of ore averaging 0.7% copper and 0.025% molybdenum. It is located southeast of Iran and currently processes 41,000 t/d. Molybdenite as a by-product is recovered in two separate stages. First, a bulk copper–molybdenum concentrate is produced and in the second stage these two are separated. The recovery of molybdenite in the first and second stages is 65% and 85–90%, respectively. The yearly production of molybdenite concentrate varies between 3500 and 4000 t. Sodium sulphide is used as the depressant of the copper and iron bearing minerals which due to a rather high consumption (17.7 kg/t) constitutes one of the major cost items of the plant (i.e., 58% of total reagents cost). Nitrogen for the plant was supplied from an oxygen plant used for the smelter through a 1400 m long pipeline. After using nitrogen in the plant for a period of 21 months, the consumption of sodium sulphide was reduced from 17.7 to 14.2 kg/t at constant metallurgy. The reduction was lower than expected which was mainly due to the type of sodium sulphide used and the lack of any automatic instrument to control the depressant (sodium sulphide) dosage.