Gold recovery comprises similar stages to the processing of most ores. First, the valuable minerals are separated from the gangue through concentration. The final concentrate is obtained by repeated processing and is smelted or leached in order to get a Dore bar. In generals, the concentration of gold includes three stages: roughing, cleaning and scavenging. The reason of concentration is to separate the raw material into two products, concentrate and tails. Ideally, in free gold recovery, all the gold will be in the concentrate and the other part will be in the tails. Separations are not perfect and in practice some waste material is reported into the concentrate and some gold particles remains in the tails. Intermediate products are called middlings and can be defined as particles that belong in either the concentrate or tails. Sometime, this product is a serious problem.
Roughing can be considered as the upgrading of the ore to produce either a low grade, preliminary concentrate or to reject tails that contain gangue at an early stage. The equipment used in this part can produce a large amount of concentrate and permit the recovery of a very high percentage of gold, produce clean tails or a combination of both. The most common equipments are cones Reichert, jigs, sluices and dry washers.
The rougher concentrate is sent to the cleaning stage in order to eliminate impurities; the process can be as simple as washing black sands by using a vanning dish. Mineral concentrates can pass through several stages of cleaning before a final concentrate is obtained. The equipment employed in this stage is the same equipment used in the rougher stage. Other equipment such as a shaking table is employed in the cleaning stage and let to obtain clean gold concentrates.
The last stage is called scavenger and consist in to process tails from rougher and cleaning stages before discarding. The material is treated through equipment that concentrates the last particles of gold. This stage is included according to the design adopted in the operation and can be simple or complex depending on the ore type. In operations where there is amalgamation, this stage is employed to recover quicksilver that otherwise will be reported in the environment. In general the equipment employed in the other stages can be used in this stage.
There are some considerations related to the concentration process. Recovery is the percentage of gold in the raw ore collected in the concentrate. For example a recovery of 85% means that 85% of the gold is reported in the concentrate and the remaining part is in the tails. A concentrate grade is the gold content in the concentrate and usually is expressed in grams per tonne (g/t) or ounces per tonne (oz/t). the ratio of concentration is the proportion of the weight of the feed to the weight of the concentrate. For example, if 500 tonnes ore feed are processed and 100 kilos of concentrate is obtained, the ratio of concentration is 5,000. If we compare this value with a mine operation whose ratio of concentration is 2,000 and the concentrate grade is similar, the second operation is economically better due to don’t need excessive raw ore in order to get a good gold concentrate.
Exist an inverse relationship between recovery and concentrate grade. This means, the higher the concentrate grade, the lower the total recovery. In general, some valuable mineral is lost in producing a high grade concentrate. Under this consideration, the higher concentrate grade is easier to refine reducing refinery costs. For each operation, a special combination of grade and recovery must be achieved to get optimum incomes.
Gravimetric concentration | Sluice | Jigs | Modified Sluice | Shaking Table | Washing plants | Spiral Concentrators | Cone Concentrator | Knelson Concentrator | Falcon Concentrator | Gemini Table | Advantages of Gold Gravity Concentration | Equipment for Gold Gravity Concentration | The Kelsey Centrifugal Jig | The APIC Jig | Multotec Spirals | Mozley Multi-Gravity Separator | Gold Recovery Using Centrifugal Concentrators | Gold Recovery by Gravity | Gravity Recoverable Gold | Determination of Gravity Recoverable Gold | Prediction of Gold Gravity Recovery | How to Calculate the Gravity Recoverable Gold | Considerations to Select a Knelson or Falcon Unit | Gold Gravity Concentration | Vickers Xatal Spirals | Centrifugal and Non-Centrifugal Gold Concentrators | Gold Recovery and Riffles | How to Include a Gold Gravity Concentration Circuit | How to Evaluate Gold Gravity Recovery | The Importance of Gold Gravity Recovery | Evaluation of Gold Recovery by Gravimetric Concentration | Importance of Gold Recoverable by Gravity | How to Clean a Gold Gravity Concentrate | Basic Gold Recovery Systems