Hydrometallurgy

The Hydrometallurgy Division (HMD) is a dynamic group within Mintek consisting of 43 professionals and technical staff. The division develops and tests hydrometallurgical flow sheets for the recovery and refining of metals from ores and concentrates. The principal areas of expertise are leaching, precipitation, cementation, ion-exchange, solvent extraction, electro-winning, and process simulations.

Gold Group

Gold and Platinum beads

Gold and Platinum beads

Gold process flow sheet development and test work has always been part of MINTEK’s technology service whilst MINTEK played a prominent role in establishing the Carbon-In-Leach (CIL) and Carbon-In-Pulp (CIP) cyanidation technology, during the 1970’s to 1980’s international gold boom. Generally the grade in available gold reserves is decreasing. This trend is accompanied by a general depletion of oxidized free-milling gold reserves, coupled to an escalation in exploitation of refractory gold ore bodies. Apart from the ever increasing complexity of upgrading processes (gravity, dense media separation, flotation, etc.), the gold leach chemistry is also becoming a progressively more complicated compromise between maximizing gold recovery and suppressing leaching of undesirable ore constituents.

Furthermore, projects such as reclamation of low gold grade tailings (containing residual precipitated cyanide, mercury and other process residues in high concentrations) or poly-metal ore bodies can be faced with problems relating to gold deportment and assaying before even considering processing options.

Pro-active engineering and design for gold projects could be challenging with regards to compliance with discharge criteria and closing of water and energy balances, which are to be linked to both national and international regulations.

MINTEK’s gold processing group specialise in process flow sheet development for new or existing gold deposits with a recent focus on refractory and low grade reclamation projects.

Basic test work would include:

  • Detailed bench scale comminution work (BBWI, SMC etc.) and milling curves
  • Understanding of the nature of the gold in the ore body as well as the host matrix of the sample, this would be done via mineralogical evaluation (SEM/XRD) combined with diagnostic leaching
  • Gravity amenability studies (Knelson GRG, qualitative Knelson tests, Falcon tests).
  • Flotation concentration amenability and detailed optimisation (Lab and pilot scale)
  • Refractory ore processing options (POX, Biox, Ozone and others)
  • Leach optimisation (reagent consumptions, optimal reagent additions, oxygen requirements, grind size evaluation, optimal carbon addition)
  • Identification of major cyanicides via detailed cyanide speciation combined with metals and other elements in solution
  • CIL/CIP or RIL/RIP kinetic isotherms and detailed plant modelling
  • Settling and/or filter tests
  • Low grade heap leach amenability testing (column tests)
  • Cyanide detox evaluations (Peroxide, SMBS, Ozone and other)
  • Post-leach solution and residue stability analysis (Acid mine drainage risks, US EPA TCLP/SPLP procedures, MINTEK gold specific sequential extraction and column tests)

Advanced Leach Facility (ALF) analysis.
Advanced Leach Facility (ALF) analysis. The ALF consists of a semi-automated mini-plant which enables the leaching kinetics of the target metal, as well as the environmental parameters, to be monitored in relation to the process. In practice the technique is very flexible and could include detailed chemical analysis or just basic parameter (gold and target metals only or together with environmental affects analysis. Furthermore, instead of terminating a leach after gold dissolution, the leach can be continued into, for example, a cyanide destruction phase with the same amount of detailed data recording. Almost all leach parameters can be adjusted at any time during operation. Specific changes can be made as the kinetic data becomes available, for example increasing agitation speed and aeration to improve dissolved oxygen concentration, or adding more cyanide to avoid free cyanide substrate limitation.