Refining of Gold and Silver-Bearing Dore

Gold and silver refining is typically done separately from mining activities, unlike platinum group metals (PGMs).

It's easier to start a gold or silver refining business compared to a platinum group metal (PGM) refinery due to readily available materials and simpler techniques.

Many independent refiners compete for mining doré, leading to low fees and advance payments.

Operating your own refinery, despite initial investment and costs, is often less advantageous and inefficient than using an independent refinery.

Harmony Gold Mine's own refinery faced challenges that led to its closure and return to independent refining.

Silver refining is usually connected with gold refining businesses, but some large operations are linked to base metal extractors.

A mixture of precious metals (especially gold and silver) obtained from smelting

Platinum group metal refiners are typically more closely connected with the extraction and mining stages of the supply chain.

Contains 30% to 98% gold, with the remainder being silver and base metals.

Contains over 50% silver, smaller amounts of gold and base metals (mostly copper and zinc).

Doré composition varies significantly due to mining location, ore characteristics, extraction methods, and processing.

A prerefining method using chlorine gas to convert base metal contaminants and silver into chloride salts, raising gold purity to ~95%.

Electrorefining step that dissolves impure gold in acid (anode) and plates out pure gold (cathode) at high purity

Dissolution/precipitation refining method, using a 3:1 mixture of concentrated hydrochloric and nitric acids (aqua regia) to dissolve the impure material.

Base metals and silver chloride salts produced during the prerefining step needing recovery and/or recycling.

Doré bars delivered to refineries differ in weight, size, and appearance.

A process using a mixture of nitric and hydrochloric acids to dissolve gold.

A reaction causing gold to form mud in an electrolyte.

A stable gold compound formed by gold being oxidized in solution containing chloride.

The process where gold dissolves at the anode during electrorefining.

The process where gold is plated onto the cathode during electrorefining.

A solution containing ions that facilitates electric conductivity.

The process where AuCl2- breaks down into metallic gold and Au3+.

The process of extracting gold from used electrolyte solutions.

Gold refining process utilizing aqua regia in the electrolytic step.

The insoluble material that forms at the bottom of the electrowinning cell due to disproportionation.

Maintaining the electrolyte's gold concentration and the concentrations of base metals and PGMs within acceptable limits

Extraction of platinum group metals (PGMs) from spent electrolytes.

The concentration of gold in the electrolyte solution, crucial for the electrorefining process

Dissolving gold using certain chemicals (aqua regia or chlorination).

A method of gold electrorefining

Plating gold onto a cathode.

There are different ways to refine silver, including electrorefining and leaching followed by precipitation.

The process of separating gold and silver from a mixture called doré using techniques like electrorefining or dissolution/precipitation.

A method of refining doré by using electricity to dissolve the gold and silver, then depositing them separately onto cathodes.

This method involves passing an electric current through a solution containing silver, causing silver ions to deposit on a cathode.

In this method, silver is dissolved from the feedstock using nitric acid, then precipitated and reduced to metallic silver.

A process that dissolves the doré in a solution and then precipitates the gold and silver separately.

This method avoids using chlorine, reducing harmful byproducts and environmental impact.

After dissolving the silver, it needs to be precipitated, meaning forming an insoluble solid from the solution.

Once precipitated, silver is further reduced to metallic silver using reducing agents like dextrose, zinc, or iron.

Maintaining consistent and reliable processes is crucial in doré refining due to the variability of the starting material.

Continual improvements are made to doré refining, especially in automation and process control.

This method directly recovers silver from the leach solution using an electric current and a stable anode.

This cylindrical electrowinning cell designed by Electrometals Corporation boasts high selectivity and automated silver harvesting.

Operators need a deep understanding of doré refining to handle the variable nature of the materials and adjust processes accordingly.

A solvent extraction-based gold refining method that aims to be cleaner and more efficient.

The EMEW process offers benefits like high selectivity, automated silver recovery, and scalability for growing needs.