Non-Ammoniacal Thiosulfate Leaching for Gold Extraction
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Solution Overview
Problem
Current methods for leaching precious metals, such as gold and silver, face challenges with the use of cyanide and ammoniacal thiosulfate processes due to toxicity, reagent consumption, and inefficiencies, particularly in treating copper-bearing ores and highly sulphidic gold ores.
Innovation Solution
A non-ammoniacal thiosulfate leaching process is developed, which includes the use of dissolved thiosulfate, copper, and a polyamine compound as a copper ligand, with optional additions of lead nitrate, thiourea, increased oxygen levels, and elevated temperatures to enhance precious metal extraction without the need for cyanide or ammonia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cyanide is used for leaching precious metals, then gold extraction efficiency is improved, but toxicity and environmental harm increase
Solution Approach 1:
The patent removes cyanide from the leaching system and replaces it with a thiosulfate-based system. The harmful cyanide component is extracted from the process, while the essential gold dissolution function is maintained through alternative chemistry involving thiosulfate and copper catalysts.
Solution Approach 2:
The patent introduces copper and polyamine compounds as intermediary catalysts in the thiosulfate leaching system. These intermediaries facilitate the dissolution of gold without requiring cyanide, thereby maintaining extraction efficiency while eliminating toxicity.
2Productivity
If ammoniacal thiosulfate is used for leaching, then precious metal dissolution is improved, but ammonia consumption and environmental toxicity increase
Solution Approach 1:
The patent removes ammonia from the thiosulfate leaching system. The harmful ammonia component is extracted while maintaining the beneficial gold dissolution capabilities through alternative means such as oxygen aeration and copper-catalyzed reactions.
Solution Approach 2:
The patent changes the chemical parameters of the leaching system by eliminating ammonia and adjusting oxygen levels, pH, and copper concentration. These parameter changes maintain leaching effectiveness while removing toxic ammonia from the process.
3Speed
If high volumes of ammonia are used to increase leaching rate, then precious metal extraction speed is improved, but reagent consumption and environmental impact worsen
Solution Approach 1:
The patent uses copper and polyamine compounds as intermediaries to catalyze the leaching reaction, replacing ammonia's functional role. This allows high leaching rates to be achieved without proportional increases in toxic reagent consumption.
Solution Approach 2:
The patent replaces the chemical mechanism of ammonia-based leaching with an oxygen-driven, copper-catalyzed thiosulfate system. This substitution maintains reaction speed while eliminating the need for large volumes of ammonia.
4Productivity
If conventional cyanide leaching is used for copper-bearing ores, then gold extraction is achieved, but copper dissolution consumes excessive cyanide and reduces extraction yield
Solution Approach 1:
The patent removes cyanide from the system and replaces it with thiosulfate, which does not suffer from the same copper interference problems. This extraction of the problematic reagent eliminates the cyanide consumption issue while maintaining gold extraction capability.
Solution Approach 2:
The patent employs copper at controlled low concentrations as a catalyst in the thiosulfate system, unlike in cyanide leaching where copper competes for reagent. The polyamine ligands selectively bind copper to facilitate gold dissolution without excessive copper consumption of the leaching agent.
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 approach reduces thiosulfate consumption, stabilizes copper, and increases precious metal extraction rates, making the process more environmentally friendly and efficient, with improved leachate treatment and reduced need for pH control.
Implementation Method 1
Thiosulfate forms a strong complex with gold (I) ions, i.e. [Au(S2O3)2]3−
Implementation Method 2
The dissolution and oxidation of copper minerals that take place when such ores are subjected to the conventional leaching process
Implementation Method 3
a polyamine compound as a copper ligand, with optional additions of lead nitrate, thiourea, increased oxygen levels, and elevated temperatures
Implementation Method 4
elevated temperatures to enhance precious metal extraction
Implementation Method 5
increased oxygen levels, and elevated temperatures to enhance precious metal extraction
Data Source
AI summary
The invention relates to modifications of a non-ammoniacal thiosulfate process of leaching precious metals (e.g. gold or silver) from precious metal-containing ores. The process involves leaching the ore with an aqueous lixiviant containing a soluble thiosulfate other than ammonium thiosulfate, a copper compound and an organic compound that serves as a copper ligand (i.e. a ligand-forming compound). Four modifications of this process are effective for increasing the amount of precious metal that can be extracted, reducing the consumption of materials, or for improving the rate of extraction. These four process, which may be used singly or in any combination, include (a) additions of soluble lead (e.g. as lead nitrate), (b) additions of thiourea, (c) increases in dissolved oxygen, and (d) increases of temperature at ambient pressure. This avoids the use environmentally harmful chemicals and allows for extraction from a variety of ores, e.g., containing substantial amounts of sulfides and/or quartz.