1997 TMS Annual Meeting: Monday Abstracts

GLOBAL EXPLOITATION OF HEAP LEACHABLE GOLD DEPOSITS: Session II: Bioleaching of Refractory Ores

Session Chairpersons: Richard D. Hagni, Chairman, Geol./Geophysics Dept., Univ. Missouri, Rolla, MO; Kenneth A. Brunk, Mineral Consultant, Former Vice President, Newmont Gold Co. Denver, CO

THE ROLE OF PROCESS TECHNOLOGY AS A KEY BUSINESS UNIT: Kenneth A. Brunk, Minerals Consultant, and Former Vice President, Newmont Gold Company, Aurora, CO 80016

This address discusses how "Mineral Processing Technology" can play a major role in the life and profitability of a mining company. Examples of past and present technological breakthroughs and their impacts will be examined. Also, the future of processing technology will be emphasized.

2:35 pm

OPERATION OF NEWMONT'S BIOOXIDATION DEMONSTRATION PLANT AND PRODUCTION OF GOLD FROM LOWER GRADE REFRACTORY ORES: R.M. Perry, F.-P. Sawyer, A.J. Schindler, M.I. Shutey, Newmont Gold Company, Carlin, NV 89822; H.B. White, Newmont Metallurgical Services, Salt Lake City, UT 841O8

Test work on biooxidation pretreatment of low grade refractory gold has been ongoing at Newmont Gold Company since 1988, including laboratory testing and pilot biooxidation heaps (400 to 25,000 st). Metallurgical results of an oxidation process utilizing Thiobacillus ferroxidans have culminated in the design, construction and operation of a 780,000 ton bioxidation demonstration facility. The facility has processed 780,000 tons of refractory ore, using a batched process with separate pads for bioxidation and ammonium thiosulfate gold extraction. Siliceous sulfide refractory (SSR) and carbonaceous (CSR) ores are treated separately during biooxidation pretreatment unit operation. Procedures and results of grinding, agglomeration and pad biooxidation cycle (180 days) are followed by lime neutralization, and dumped on oxide leach pads, or stacked on the ammonium thiosulfate leach pad. Gold is leached with either cyanide for SSR ores or ammonium thiosulfate for preg-robbing CSR ores.

3:00 pm

BIOLEACHING AND PROCESSING OF A REFRACTORY GOLD ORE: N.S. Lynn, Lyntek, Inc., 775 Mariposa Street, Denver, CO 80204

A new process has been developed to bioleach refractory gold ores to expose the precious metal values using Thiobacillus ferrooxidans bacteria. The ore is hosted in a limestone rock with secondary replacement of carbonaceous and pyritic minerals. Crushing, stacking, bioleaching, rinsing and neutralization have been completed in a 45-day total time cycle. The use of sulfuric acid operation, and concentrated Thiobacillus ferroxidans population allows the short bioleaching cycle. The ore is then processed using conventional carbon-in-leach cyanide recovery techniques.

3:25 pm BREAK

3:35 pm

OXYGEN DIFFUSION INTO WET ORE HEAPS IMPEDED BY WATER VAPOR UPFLOW: R.W. Bartlett, K.A. Prisbrey, Univ. of Idaho, College of Mines and Earth Resources, Moscow, ID 83844-3025

Natural bioxidation of shallow, refractory ore heaps, relying on gaseous oxygen diffusion from the heap surface is attractive because of its simplicity and potential low cost, especially without using a lined pad, which is possible if percolation of leachate through the heap is avoided. In this case, the excess oxidation enthalpy must be removed by water evaporation from within the wet ore heap, and the rising water vapor flux within it will impede the downward oxygen flux. An analysis of this process shows that for typical values of pyrite grades and limited temperature increases. In the ore heap, the oxidation rate and penetration into the heap is reduced to values between about 30 percent and 50 percent of those obtained when leachate percolation occurs and water evaporation is not significant mechanism of heat removal.

4:00 pm

ECONOMIC CRITERIA FOR CHOOSING BIOHEAP PRETREATMENT OF MIXED OXIDE/REFRACTORY GOLD ORE: Robert W. Bartlett, Univ. of Idaho, College of Mines & Earth Resources, Moscow, ID 83844-3O25

Bioheap pretreatment of sulfidic refractory gold ore prior to cyanide leaching is a promising new technology, especially for low-grade ores that cannot be oxidized by pressure leaching or roasting. Ores containing both refractory and amenable gold require economic decisions whether, or not, to pretreat before cyanide leaching. This choice is more complex than familiar ore/waste cut-off grade decisions. Pretreatment may increase recovery but delays receiving revenue. An equation has been developed that computes a "critical cyanide leachable gold grade" for determining whether pretreatment will be profitable. If the ore's actual cyanide leachable grade, without pretreatment, is above critical grade, pretreatment will not pay. The parameters in this equation are: waste/ore cut-off grade, pretreatment yield, total gold grade, pretreatment operating cost and project's financial discount rate. Calculations are provided for use in mine development planning when bioheap pretreatment is an available option.