Thiosulfate Gold Silver Extraction with Electrochemical Recovery
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Solution Overview
Problem
Existing gold and silver extraction methods from ores and concentrates are energy-intensive, require high temperatures and pressures, and do not effectively recycle thiosulphate solutions, leading to low concentrations of precious metals and residual waste.
Innovation Solution
A process using a sodium thiosulphate solution with ammoniac and bivalent copper salt as catalyst for leaching gold and silver, followed by electrochemical separation and recycling, and subsequent acid leaching to produce a high-purity Au-Ag alloy, with the use of insoluble electrodes and sulphuric acid leaching to recover copper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxidation process is performed at high temperatures and pressures in autoclaves, then gold and silver leaching efficiency is improved, but energy consumption increases and equipment complexity increases
Solution Approach 1:
The invention changes the operating parameters from high temperature and pressure (conventional autoclave conditions) to ambient or mild conditions by using a different chemical mechanism - thiosulphate complexation with copper catalysis, which allows efficient leaching without extreme conditions
Solution Approach 2:
The invention replaces the mechanical/thermal oxidation system (autoclaves with high temperature and pressure) with a chemical complexation system using thiosulphate and copper catalyst, eliminating the need for high-energy equipment while achieving comparable or better leaching efficiency
2Ease of manufacture
If thiosulphate solution is not recycled, then process simplicity is maintained, but waste generation increases and environmental harm increases
Solution Approach 1:
The invention implements a recycling system where thiosulphate solution containing dissolved gold and silver is recovered from the leaching process, and the precious metals are extracted through electrochemical methods, allowing the thiosulphate solution to be reused and preventing waste discharge
Solution Approach 2:
The invention creates a closed-loop system where the output of the leaching process (thiosulphate solution with dissolved metals) is fed back into the system through electrochemical recovery, and the regenerated thiosulphate solution is returned to the leaching circuit, establishing continuous material circulation
3Productivity
If conventional separation methods are used, then gold and silver are extracted from solution, but the concentration of precious metals in final product is low
Solution Approach 1:
The invention replaces conventional separation methods (adsorption, cementation, precipitation) with electrochemical separation using insoluble electrodes, which provides more efficient metal recovery and higher concentration in the final product through direct electrical deposition
Solution Approach 2:
The invention uses an electrochemical cell with insoluble electrodes as an intermediary system that selectively deposits gold and silver from the thiosulphate solution, concentrating the precious metals to high levels while leaving the thiosulphate solution to be recycled
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves efficient extraction of gold and silver with high purity (99.9%) while recycling reagents, reducing energy consumption and waste generation, and is applicable for low-grade materials, with global efficiencies of 78.2% for gold and 76.1% for silver.
Implementation Method 1
a process for chemical extraction of gold and silver from ores, refractory pyritic concentrates, flotation tailings and metallurgical slag by using as reagent a sodium thiosulphate solution in the presence of ammoniac and of a bivalent copper salt as catalyst
Implementation Method 2
The separation of gold and silver from thiosulphate solutions is achieved by adsorption on ion exchangers, activate carbon, electrochemical processes
Implementation Method 3
subsequent acid leaching to produce a high-purity Au-Ag alloy, with the use of insoluble electrodes and sulphuric acid leaching to recover copper
Data Source
AI summary
The present invention relates to a process for chemical extraction of gold and silver from low grade and refractory pyritic concentrates containing minimum 1 ppm Au, by their leaching in enameled cast iron reactors, steel plated lead or plastic coated steel, at room temperature, in ammoniac solutions (pH 8-10) of sodium thiosulfate (50-60 g/l Na2S2O3. 5 H2O) with a divalent copper salt as catalyst (3-4 g/l Cu). The suspension resulting after 2-4 hours of reaction is filtered. The thiosulfate solution containing minimum 5 mg/l undergoes an electrolysis process with insoluble anodes. Copper, gold and silver is deposited in the cell as a sludge, and the electrolyte having a maximum content of Au of 1 mg/l, is recycled to the leaching operation of raw material, after correction of copper content and alkalinity to the baseline values. The copper, gold and silver deposit, separated as a sludge, is purified by leaching copper in a solution of 30-40% sulphuric acid at a solid:liquid ratio of 1:5-1:10, at a temperature of 85-90° C. for 2-4 hours under air bubbling. The suspension is filtered. The copper leached as CuSO4.5H2O returns to the extraction process of gold and silver.