Every month, we put out a Fine Grind article in Mining Engineering to keep members in touch with the latest happenings, technical updates and other interesting news from the MPD division. This is the Fine Grind that appeared in the May 2017 issue. We invite you to comment, discuss or ask questions!
Amy Jacobsen, Secretary Treasurer
2017-2018 Mineral & Metallurgical Processing Division Executive Committee
May 2017 Fine Grind
SME Mineral Processing and Extractive Metallurgy Handbook Coming in 2018
by Scott Shuey, Second Regional Vice Chair, MPD Executive Committee
Many of the MPD Membership may be aware that SME is assembling a new edition of the Mineral Processing Handbook. Under the auspices of Rob Dunne, Courtney Young and S. Komar Kawatra, experts and industry leaders from around the globe are being amassed to produce an update to the cornerstone of every process engineer’s library. With the volumes slated for publication in 2018, snippets of various chapters will be periodically presented here in the Fine Grind as a hint of what is to come.
PRESSURE LEACHING and PRESSURE OXIDATION
Rudi Frischmuth, Tom Krumins, Murray Pearson, Kevin Fraser
Pressure leaching and pressure oxidation are hydrometallurgical processes applied to the extraction of many metals. The processes occur above atmospheric boiling temperature and pressure, require a sealed reactor vessel, and often operate in highly corrosive and oxidizing environments. Pressure leaching and pressure oxidation have been applied to multiple processes with a wide range of conditions, but include similar aspects such as:
- Slurry Feed: chemical conditioning, preheat, high-pressure pumps.
- Reactor Vessel: digester, leach or oxidation autoclave.
- Pressure Letdown: flash vessel.
- Off-gas Handling: atmospheric condenser and scrubber.
- Ancillary Systems: acid, oxygen, air, steam, water injection systems, agitator seal system.
Pressure leaching is primarily applied when the goal is to solubilize desirable elements, recover the solution fraction, and reject the residual solids. The process can operate under alkaline or acidic conditions and may include the use of oxygen gas (or an alternative oxidant such as hydrogen peroxide) to oxidize and leach base metal sulfide minerals. The most common alkaline pressure leach processes are applied in the extraction of alumina (e.g., Bayer process), tungsten, uranium, rare earth elements (REEs), as well as nickel, cobalt and copper sulfide minerals. The most common acidic processes are applied in the extraction of platinum group metals (PGMs), nickel-cobalt laterites and uranium, as well as copper, nickel, cobalt, molybdenum and zinc sulfides. Acidic pressure leaching of iron from an ilmenite slag to produce synthetic rutile is a pressure leaching process where the solid fraction contains the product and the solution is rejected (recycled).
Pressure oxidation is applied when the objective is to decompose sulfide minerals for the recovery of desirable elements from the solids fraction, and rejection of the solution fraction. Pressure oxidation is mostly applied to refractory gold-bearing ore or concentrates where the gold is locked in the sulfide minerals and recovery using a conventional cyanide leaching is not effective. The process is mostly operated under acidic conditions; however, alkaline pressure oxidation is also practiced.
This chapter provides a review of pressure leaching and pressure oxidation unit process systems, including discussion on the key process design aspects, metallurgical test work, key economic drivers for operating and capital costs, and typical practices for equipment selection and design.