Projects
Lluvia de Oro / La Jojoba
NWM Copper
NWM Copper
Minera Columbia has commissioned the ASPN (Acidification, Sulfidation, Precipitation, and Neutralization) system for laboratory test work to develop a low cost process for removing the copper component in the gold bearing solutions from the leach pad. The adsorption circuit of the ADR plant would otherwise become overwhelmed by the copper concentration in the solution and hence the ASPN system is being developed for copper removal without affecting the gold bearing component.

The standard SART process that exists today is complicated and expensive to operate. It is hoped that the ASPN system will become a low cost alternative that creates a salable copper sulfide concentration with cyanide recovery and can be operated at a profit for the mine. Utilizing a SART process is break even at the best of conditions and usually operates as a loss to the operation per current budgetary forecasts.

The solution currently being utilized for test work comes from the cold strip tank in the desorption circuit. The cold strip process removes the copper that has loaded onto the carbon in the adsorption columns and concentrates the copper in the cold strip tank. Once the cold strip is completed, the solution is pumped by a peristaltic feed pump, 0.1-5.0 gallons per minute into the tube reactors.

The tube reactors consist of one inch pvc pipe for the H2SO4 injection point, four inch pvc pipe for the NaHS injection point, returns to one inch pvc pipe for continued flow to the one tonne tote settling tank and then exits the tote for discharge back into the solution pond. The settling tank is the point where copper removal is expected in the form of Cu2S. This final product has a salable cash value. The diagram indicates 90 degree turns in the piping and these are deliberately placed in line as mixing points for the reagents. The 90 degree elbows disrupt laminar flow and are part of current thinking for design criteria for commercial operation.

The tube reactor is a closed circuit and has been designed as such for the control of hydrogen cyanide gas (HCN). HCN is generated in the first step when H2SO4 is added, as the pH is lowered to 3.0-5.0. At this point in time the optimum pH has been determined to be 4.0 and has the potential to release HCN into the surrounding environment if not controlled in the proper manner. By keeping the system as a closed loop the potential to create a hazardous situation has been dramatically reduced. The biggest point of concern, at this time, is the discharge point into the process pond. By discharging the solution below the water line in the process pond it allows for the discharged solutions pH to return to above pH 9.0 which removes the potential for HCN generation and returns the cyanide from the HCN state back within parameters for stable control of NaCN. Previous test work by others parties has determined that the HCN created within a closed loop holds the HCN within a gaseous state within the solution similar to dissolved oxygen in water. Therefore as long as the system is operated as a closed loop the HCN can be controlled.

Ongoing test work is planned for reducing the settling time needed for the Cu2S crystals removal from the solution. At this point in time the settling rate to achieve 85% copper removal requires 1250 minutes within the settling tote. Future work is planned for the trials of filters, cyclones, and/or the injections of alum as a catalyst to speed up the copper sulfide settlement rate. Alum is used in the water treatment industries and could assist in enhancing the ASPN process. The company has recently hired a metallurgical technician for continued monitoring of the test work. KCA in Reno, Nevada, Keith Huck from Boise, Idaho, and Bruce Thorndycraft from Idaho City, Idaho have been retained for technical support during this testing stage. The process development deadline is scheduled for September 2011 to allow for EPCM and completion of the commercial project by March 2012.