• GEOCOAT^®
• Process Overview
• Design Concept
• Pad and Ponds
• Support Rock
• Coating and Stacking
• Irrigation and Solution Management
• Aeration and Temperature Control
• Solution Treatment
• Heap Reclaim and Concentrate Separation
• Water Balance
• Inoculum
• GEOLEACH™
• HotHeap™

GEOCOAT^® Process Overview

The GEOCOAT^® process uses iron- and sulfur-oxidizing microorganisms to facilitate the oxidation and leaching of sulfide minerals in an engineered heap environment.

In the GEOCOAT^® process, sulfide flotation or gravity concentrate is coated onto crushed and sized medium to support the concentrate during the biooxidation cycle. This medium, hereinafter referred to as "support rock," can be barren or may contain sulfide or oxide mineral values. The coated material is stacked on a lined pad. Low-pressure air blown up through the heap provides oxygen for the reactions and controls the heap temperature. The heap is irrigated with recycled effluent solution that carries bacteria, ferric iron and nutrients for the bacteria. The oxidized concentrate (in the case of refractory gold) and/or the pregnant leach solution (in the case of base metals) is further processed by conventional means for metal recovery.

Simplified GEOCOAT^® Flow Diagram for Gold-Copper Concentrate

The relatively uniform size of the support rock particles results in large interstitial spaces within the heap, which provide low resistance to air and solution flows. Low-pressure fans supply air through a system of perforated pipes placed under the heap. The airflow rate is adjusted to control the temperature within the heap to the optimum range for bacterial activity. The air also provides the oxygen necessary for the oxidation reactions.

The large interstitial spaces, combined with the thin concentrate layer, create ideal conditions for biooxidation. The sulfide mineral grains and the attached bacteria are constantly exposed to the downward flowing solution, and the countercurrent flow of air. This results in the efficient transfer of oxygen and rapid oxidation rates. Oxidation is typically complete within 45 to 120 days, depending on the mineralogy.  After biooxidation, the heap is reclaimed and the concentrate is separated from the support rock by wet screening. The washed support rock is recycled for re-coating with fresh concentrate.