Improvement of Gold and Silver Recuperation from Low-Grade Solutions Through Mixed Process: Desorption Zadra and Merrill Crowe

摘要

During beneficiation metallurgical plant operation different conditions can affect the process. These variations or new conditions often require modifications to operational criteria or complements of different processes to the actual, in order to maintain or improve production rates. In the present case study, a mining company in Peru, that exploits a low sulfidation epithermal Au-Ag deposit, uses a heap leaching process to extract the valuable minerals, and after that, recover them through precipitation technology with zinc called Merrill-Crowe. During the first years of operation, the content of Au and Ag dissolved in the solution were high, so the minerals were quickly recovered due to the first levels of the leaching pad. However, the increase in area, pad height and the irrigation of exhausted (aged) cells generated a low-grade Au- Ag solution (intermediate solution) in the transit of the percolation solution. This solution was mixed with the rich solution generating high flow to be treated in the Merrill Crowe plant, causing an increase in operating costs. A balance solutions study was realized to obtain Au-Ag content and flow rate that was economically unfeasible to be treated in Merrill-Crowe process plant but feasible to carry it to a recover process with less cost, using activated carbon (CIC).After several metallurgical tests, we concluded that it is necessary an adsorption plant through activated carbon in column (CIC) and desorption process (pressurized Zadra) to make possible recover the gold and silver of new solutions (low-grade solution). The concentrated solution from the Zadra recovery plant, produced from low-grade solutions, should enter to Merrill-Crowe plant and as a result, it would optimize the consumption of metallic zinc dust, thus obtain a cleaner precipitate for processing in foundry. Finally, beneficiation plant that has Merrill Crowe process, now has an activated carbon plant additionally.The project investment was 7.8 Mills US$ and the new plant produced 19,500 oz of gold and 155,000 oz of silver. The project obtained an NPV of 18.6 Mills US$, an IRR value of 100 % and a payback period of fifteen months.