In Situ Thiosulfate Generation for Gold Recovery
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Solution Overview
Problem
Conventional cyanidation processes for gold recovery face challenges with high reagent consumption, environmental concerns, and inefficiencies in extracting gold from sulfidic and carbonaceous ores, particularly due to preg robbing and double refractory nature of certain ore types, leading to high costs and gold losses.
Innovation Solution
A process involving partial oxidation of sulfidic ores to produce elemental sulfur, which is then reacted with sulfite or bisulfite to generate thiosulfate lixiviant in situ, allowing for efficient gold recovery using thiosulfate leaching, reducing reagent costs and environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cyanidation process is used for gold recovery, then gold can be solubilized and recovered, but high reagent consumption and environmental harm occur
Solution Approach 1:
The patent replaces cyanide with thiosulfate as the lixiviant, fundamentally changing the chemical parameter of the leaching agent. Thiosulfate leaching operates at different pH ranges (9.0-11.0) compared to cyanidation (9.5-11.0) and uses different complexing mechanisms, thereby achieving gold recovery without the environmental toxicity associated with cyanide
Solution Approach 2:
The patent employs inexpensive reagents including sodium thiosulfate, copper sulfate, and ammonia to create an environmentally benign leaching system. These reagents are less hazardous and can be handled more safely than cyanide, reducing environmental risk while maintaining gold recovery effectiveness
2Productivity
If cyanidation is used on sulfidic ores, then gold recovery is attempted, but oxygen and acid consumption increase and operating temperatures rise
Solution Approach 1:
The patent modifies the chemical environment by introducing thiosulfate instead of cyanide, which changes the reaction kinetics and reagent consumption patterns. Thiosulfate leaching requires different oxygen concentrations and acidification levels compared to cyanidation, thereby reducing the metabolic burden on the bioleaching system
Solution Approach 2:
The patent uses thiosulfate as an intermediary complexing agent that facilitates gold dissolution without requiring the extreme conditions needed for cyanide leaching. Thiosulfate forms stable gold complexes under milder conditions, acting as a mediator that reduces the need for high oxygen and acid inputs
3Productivity
If thiosulfate leaching is used, then gold recovery improves on sulfidic and carbonaceous ores, but reagent losses occur due to oxidation to polythionates or sulfates
Solution Approach 1:
The patent implements a reagent regeneration system where polythionates and sulfates produced during leaching are converted back to thiosulfate. This closed-loop feedback mechanism recycles the oxidized thiosulfate species, reducing the need for continuous fresh thiosulfate addition and minimizing reagent loss
Solution Approach 2:
The patent recovers and regenerates thiosulfate from oxidation products (polythionates and sulfates) through chemical reduction processes. Instead of discarding the oxidized reagents, they are converted back to active thiosulfate form, thereby recovering valuable reagent and reducing waste
4Productivity
If ammonium thiosulfate is used for leaching, then gold dissolution occurs, but environmental concerns arise from copper and ammonia presence
Solution Approach 1:
The patent adjusts the pH range to 9.0-11.0 and controls copper concentration to optimize gold dissolution while minimizing environmental impact. By carefully controlling these parameters, the system achieves effective leaching with reduced toxicity compared to conventional cyanidation or ammonium thiosulfate systems
Solution Approach 2:
The patent employs sodium thiosulfate instead of ammonium thiosulfate, eliminating ammonia from the system. Sodium thiosulfate is equally effective for gold dissolution but does not produce ammonia emissions or require copper catalysis, thereby reducing environmental concerns while maintaining leaching efficiency
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 decreases oxygen and acid consumption, lowers operating temperatures, and effectively recovers gold from refractory sulfidic and carbonaceous ores by generating thiosulfate in situ, improving process economics and reducing gold losses.
Implementation Method 1
reacted with sulfite or bisulfite to generate thiosulfate lixiviant in situ
Implementation Method 2
partial oxidation of sulfidic ores to produce elemental sulfur
Implementation Method 3
efficient gold recovery using thiosulfate leaching
Data Source
AI summary
Precious metal recovery by thiosulfate leaching where thiosulfate lixiviant is generated in situ employing elemental sulfur generated from partial oxidation of sulfidic precious metal-bearing feed and/or employing reactants from processing effluent.