It is important to determine the economic recovery of gold, especially when the final product is gold concentrate, which will be commercialized. The metallurgical efficiency of gold concentration operation is difficult to express because there are two criteria of performance, specifically, gold concentrate grade and gold recovery. Neither of these alone gives an indication of the effectiveness of an operation, and if they are combined in some formula or relationship, there are several variables that have influence. Since milling is an operation performed as one or two steps in most profitable overall methods of producing a gold product, the main objective of the mill operation should be to make a maximum contribution to this maximum profit.
When gold concentrates are sold to the custom smelters, the income from the operation, and the costs, may be determined. When gold concentrates are further processed by another process, and it is difficult to establish a formal financial relationship between the milling and smelting areas of the gold company, the mill superintendent’s job is less well defined. But even so, if the mill superintendent works as though he were selling the gold concentrate, and uses reasonable conditions of sale, then it will be possible to get a good indication of the effectiveness of the operation by calculating the economical recovery of gold.
The economic recovery indicates a financial measurement of an operation, a figure or consideration that may be used to compare, week by week, month by month, the money making capacity of the operation, even when there is significant change in the gold grade or operating conditions due to the complexity of the gold ore. For example, a 1.5 g/t of gold and 200 g/t of silver ore, would provide a gold concentrate weighing 6% of the feed and assaying 180 g/t of gold and 40,000 g/t of silver. This concentrate is shipped to appropriate smelters, freight and treatment charges and payments calculated and the net return obtained. This is the optimum financial return for the operation of the gold recovery plant and may be used as a standard. The return for the actual, real-life, gold mill operation is calculated in the same way, and the ratio of the two termed the economic gold recovery of the particular plant.
Many additions and modifications may be made in any particular case. For example, extremely fine intergrowth between gold bearing minerals and gangue will reduce the final concentrate grade, and its value is affected. Also, other aspect, sometimes overlook is the moisture content. Some gold flotation plants employ cheap filtration equipment, whose operating efficiency is low. This situation obliges to transport a gold concentrate with more water than necessary. This excess of water creates penalties on the concentrate. The efficiency of separation has a definite physical significance in that it represents the proportion of feed material that is completely separated by a concentration process. Because of this, the separation efficiency is simply the difference between the percentage unit recoveries of any two defined constituents in any one product of a separation. Separation efficiency is a very useful and practical concept for investigating and comparing gold concentration processes.