Flotation Reagent System Hazard Classification:

During engineering for a large Mexican mill expansion, the owner retained Argo Consulting to review the xanthate and dicresyl dithiophosphate mix-feed system hazard classifications assigned by the EPCM. Chemical hazard classifications determine the mechanical controls and electrical code standards to ensure personnel and plant safety. Setting standards that are too stringent makes the cost of meeting the classification excessively expensive and challenging. Xanthate molecules hydrolyze (break down) generating CS2 in the process that rapidly volatilize creating potentially explosive conditions. Argo determined an operating plan that allowed a non-hazardous classification, saving significant installation costs as well as preventing a retrofit of the older plant system. A breakdown product of dithiophosphate degradation product, although typically an insignificant possibility, is H2S which poses health problems at low atmospheric concentrations and an explosive hazard at higher concentrations. Unfortunately the dicresyl dithiophosphate product specified by the mine can be unstable, although posing a low probability of breakdown, Argo assessed that there was some risk and a normal H2S product classification was necessary.

Flotation circuit optimization:

A significant USA Pb-Zn-Ag mill had process improvement opportunities to capture and equipment obsolescence issues to contend. Bill Hancock developed a practical plan for froth washing to improve lead concentrate grades that offered significant shipping cost reductions. Results and metallurgical observations made during the froth sprinkling evaluations lead to followup QemScan mineralogical analyses that showed significant metallurgical opportunities could be obtained through flowsheet optimization. Subsequent plant flowsheet modifications were tested on the existing old circuit by actually redirecting flows to simulate different flowsheets and circuit residence times to assess metallurgical impact. Lab float tests were conducted in conjunction to assess optimum metallurgical targets.

From that work the entire flotation circuits were replaced with higher conventional cell capacities on both the Pb and Zn circuits, additional flotation columns were installed on both the Pb and Zn circuits, Pb and Zn unit cells were installed and cleaner scavenger circuits were installed. Results: increased Pb recoveries ~ 5%, increased Zn recoveries over 10% with higher and more consistent concentrate grades, and Ag recoveries increased by 2%+.

Mill operator flotation training

Argo Consulting has provided several classroom courses to clients for flotation and process circuit operators which provides simple mineral processing fundamentals to help them understand the basics and provide them a perspective and understanding to improve their circuit control. Providing several operators this training at a time and away from the operation facilitates improved understanding and coordination between operators as well as provide a commonality for that coordination. This training has been considered valuable by the several clients this program has been provided. Further information on this training is provided on the Argo Operator Training webpage.

Potash flotation gypsum reduction and KCl recovery improvement

A USA potash mine utilizes flotation to separate very coarse KCl from NaCl from a mixed salt evaporate. Because of calcium contamination the potash product had sufficiently high levels of insoluble gypsum that posed a sedimentation problem when the KCl was dissolved by formulators. Hancock was hired to identify a gypsum flotation depressant and prove the effectiveness in plant testing. This was successfully accomplished and the assignment continued with technical and operations flotation training. The data collected from the depressant plant evaluations was further used the consultant for metallurgical modeling that lead to determining that the flotation capacity provided insufficient residence time to maximize KCL recoveries. Reducing the plant feedrate resulted in a significantly increased KCl annual production tonnage.