Two-Step Sulphide Leaching to Cut Cyanide Use
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Solution Overview
Problem
Existing mineral leaching processes face issues with elemental sulfur consuming cyanide and forming thiocyanates, leading to increased costs and environmental concerns, and precious metals being locked in reaction products, resulting in poor recovery during cyanidation.
Innovation Solution
A two-step leaching process is employed, first at a pH of less than 4 to form a slurry with elemental sulfur, followed by a second leaching step at pH 9.0 to convert sulfur into thiosulphate, which leaches precious metals, minimizing thiocyanate formation and enhancing recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cyanidation is used to recover precious metals from leach residue, then precious metal recovery is achieved, but elemental sulfur consumes cyanide forming thiocyanates, increasing cyanide consumption and operating costs
Solution Approach 1:
The patent applies preliminary action by conducting an oxidative leaching step at pH 9.0-11.0 before cyanidation to convert elemental sulfur to thiosulfate. This preliminary treatment prevents sulfur from consuming cyanide in subsequent cyanidation, thereby reducing cyanide consumption while maintaining precious metal recovery efficiency
Solution Approach 2:
The patent converts the harmful effect of elemental sulfur (which consumes cyanide) into a beneficial outcome by oxidizing it to thiosulfate. This transformation eliminates the harmful cyanide-consuming reaction while the thiosulfate formed can actually contribute to precious metal leaching, thus converting a problem into an advantage
2Ease of manufacture
If cyanidation is used to recover precious metals, then metal recovery process is simple, but thiocyanates are generated which are difficult to destroy in conventional detox systems, creating environmental issues
Solution Approach 1:
The patent converts the harmful elemental sulfur that generates environmental problems (thiocyanates) into beneficial thiosulfate through oxidative leaching. This eliminates the source of harmful thiocyanates while maintaining process simplicity by integrating the oxidation step into the existing flow
3Productivity
If oxidative leaching at pH 9.0 is performed to convert sulfur to thiosulphate, then cyanide consumption is reduced and precious metal recovery is improved, but process complexity increases with an additional leaching step
Solution Approach 1:
The patent merges the oxidative leaching step with the existing acid leaching operation by using the same reactor and combining the chemical functions. This integration approach adds the necessary sulfur conversion functionality without requiring completely separate equipment, thus managing process complexity while achieving improved metal recovery
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
The process effectively recovers precious metals by converting elemental sulfur into thiosulphate, reducing cyanide consumption and environmental impact, while improving metal extraction efficiency.
Implementation Method 1
The objective of the Albion Process is oxidation of sulphides to allow liberation of metals for downstream recovery
Implementation Method 2
subjecting the slurry or pulp to oxidative leaching at pH of at least 9.0 to thereby form thiosulphate, whereby the thiosulphate leaches precious metal from the solid residue
Implementation Method 3
subjecting the slurry or pulp to oxidative leaching at pH of at least 9.0 to thereby form thiosulphate
Data Source
AI summary
A process for leaching minerals that contain metal sulphides and one or more precious metals or precious metal compounds, the process comprising the steps of a first leaching step to leach the minerals under oxidative conditions at a pH of less than 4 to form a slurry or pulp, the slurry or pulp comprising a solid phase containing unreacted components, solid reaction products and elemental sulphur, and subjecting the slurry or pulp or solid residue from the first leaching step to a second leaching step comprising oxidative leaching at pH of at least 9.0 to thereby form thiosulphate, whereby the thiosulphate leaches precious metal from the solid residue.