Choosing the best gold processing method for your project is the most important decision you will make. Through decades of industry experience combined with technological advancements, Sandreck has developed a complete assessment model to assist miners and operators in choosing the most effective and profitable processing path.
Knowing Your Ore
To select a process for you, it is essential to have a clear understanding of what you are processing. The characteristics of your ore (e.g., mineralogy, mineral / commodity liberation, mineral assemblages, etc.) will have the most influence on the viable processing options. A primary goal of this model is to have a complete ore characterization program.
1. Gold Characteristic:
- Free-Milling Gold: The gold is liberated or exposed once the ore is ground. Therefore, free-milling gold can be conventionally leached using cyanide with relative ease. This is the best and simplest scenario.
- Refractory Gold: Gold is locked in sulfide minerals (e.g., pyrite, arsenopyrite) or chemically bound. Refractory gold will result in very low recovery with direct cyanidation and requires pre-treatment.
- Gold Particle Size: Is the gold “visible” (coarse) or “invisible” (sub-microscopic)? Coarse gold can be recovered via gravity, while fine-grained gold is leached.
- Leaching: This ore has carbonaceous material that absorbs the gold cyanide complex, depriving it from the solution.
2. Gold Composition:
- The non-valuable minerals in ore (i.e., gangue) can be a significant impediment to processing.
- Sulfide content: High levels of sulfides will lead to a refractory ore and require oxidation (e.g., roasting, bio-oxidation, or pressure oxidation).
- Organic Carbon: As mentioned, organic carbon causes preg-robbing and must be neutralized.
- Clays and sliming minerals: cause viscosity problems in the leaching tanks, reduce filtration performance, and can consume large amounts of reagents, therefore affecting the reagents’ cost.
- Deleterious elements: Arsenic, mercury, etc., pose significant handling and environmental issues while influencing waste treatment choice.
Common Gold Processing Methods
- Gravity separation: This technique is the oldest method in the world of gold recovery. The gravity methods remove free gold prior to leaching, which not only assists with the overall recovery, it also decreases the average overall cost per ounce in the processing plant.
- Cyanide leaching (Cil/Cip): Cyanide leach processing is the industry standard for free-milling ores. The ore will be ground to a slurry and agitated with a dilute cyanide solution, thereby oxidizing the gold, and the dissolved gold is quantified in solution.
- Flotation: Primarily a method for sulfide ores. Flotation separates the sulfide minerals (and equally the locked gold) from the crude ore and forms a hydrophobic concentrate of sulfide minerals.
- Roasting: The cooling process has traditionally been the favored methodology, oxidation of sulfide, high capital costs, economically, but environmental issues (SO2 and arsenic emissions).
- Non-Cyanide leaching: For particular projects where the use of cyanide is restricted or banned, or for specific ore types. Non-cyanide methods are typically more expensive and less efficient than cyanide, but are valuable or niche.
The Assessment Model: A Step-by-Step Framework
Our model is an iterative decision-making framework designed to eliminate uncertainty.
Phase 1: Gold Testing (What Is It?)
Anything always starts with data. This model conducts a rigorous program of test work on representative ore samples:
Fire Assaying: For accurate head grade.
Gravity Recoverable Gold (GRG) Test: Determines the proportion of gold recoverable by gravity.
Diagnostic Leach Test: The most critical test. It sequentially leaches the ore to determine how much gold is free-milling, associated with sulfides, or locked in silicates. This directly dictates the process flow sheet.
Flotation Test Work: If sulfides are present.
Preg-Robbing Test: To identify carbonaceous material.
Phase 2: Technical Scoping (What Can We Do?)
The data from Phase 1 is used to screen technically viable process options. A high GRG value mandates a gravity circuit. A diagnostic leach showing >80% free gold points to direct cyanidation.
High sulfide content with low gold liberation points to flotation and pre-treatment. The engineers will develop 2-3 technically sound flow sheet options for further analysis.
Phase 3: Economic and Environmental Modeling (What Should We Do?)
Here we make the move from technical possibility to economic reality. For each viable flow sheet, we will model:
- Capital Expenditure (CAPEX): Equipment, construction, and infrastructure.
- Operating Expenditure (OPEX): Reagent consumption, energy, labor, and maintenance.
- Projected Recovery and Revenue: Based on the results of test work.
- Environmental Footprint and Permitting Risk: Water consumption, tailings management, toxicity of reagents (e.g., cyanide vs. thiosulphate), emissions.
- Net Present Value (NPV) and Payback Period: The ultimate financial metrics for making the decision to go ahead.
Phase 4: Pilot Scale Verification and De-Risking (Prove It)
For larger projects, and most projects using new and/or high-risk technologies — such as POX or BIOX — we would highly recommend continuous pilot plant testing.
Running 10-100 tons of ore through a miniaturized version of the proposed plant reduces project risk by validating metallurgical performance, obtaining large bulk samples of tailings and products, and providing accurate data to facilitate final engineering design.
The assessment model provides a systematic, objective, and data-driven pathway to this important step. It commits its users to the systematic characterization of an ore body, reviewing all technical forms of alternatives, and modelling the economic performance of these alternatives.
The day you launch a new gold (or any other) project, you expect a return. Work with Sandreck – mining machinery manufacturer in China, from ore characterization to the selection of a final process option, we provide professional service.
