Integrated Copper Leach Process Managing Arsenic and Silver Recovery
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Solution Overview
Problem
Current copper recovery processes from sulphidic feeds containing iron, arsenic, and silver face challenges such as low silver recoveries due to the formation of insoluble silver jarosites and copper arsenates, which lead to environmental instability and increased operating costs, particularly in pressure oxidative leaching and subsequent cyanide leaching steps.
Innovation Solution
An integrated process combining low acidity, low solids pressure leaching with copper heap leaching, where copper is recovered by forming stable iron arsenic compounds during pressure oxidative leaching, maintaining a temperature above 200°C, and recycling solutions to manage water balance and acid levels, allowing for autothermal operation and reducing the need for lime boil steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pressure oxidative leaching is used to recover copper from sulphidic feeds containing iron and arsenic, then copper dissolution is improved, but copper may precipitate as insoluble copper arsenate leading to copper losses
Solution Approach 1:
The process applies preliminary anti-action by controlling the Fe:As molar ratio to be greater than 4:1 before pressure oxidative leaching begins. This pre-established iron excess prevents copper arsenate precipitation from occurring in the first place, rather than attempting to remediate it afterward. The iron acts as a sacrificial component that preferentially forms stable iron arsenate compounds, protecting the copper from forming insoluble precipitates.
Solution Approach 2:
The process utilizes parameter changes by carefully controlling the Fe:As molar ratio parameter to maintain values greater than 4:1 throughout the pressure oxidative leaching operation. This parameter control ensures that iron remains in excess to form stable iron arsenate compounds (scorodite or basic ferric arsenate sulphate) rather than allowing copper arsenate precipitation. The temperature is also controlled to be above 200°C to optimize the leaching reaction while maintaining the desired precipitate stability.
2Productivity
If silver is processed by pressure oxidative leaching, then gold recovery by cyanide leaching is improved, but silver forms insoluble silver jarosites resulting in low silver recoveries
Solution Approach 1:
The process converts the harmful formation of silver jarosite into a beneficial intermediate state. Instead of viewing silver jarosite formation as a problem to be eliminated, the process accepts it as an expected outcome of pressure oxidative leaching and then uses a subsequent lime boil step to selectively destroy the jarosite structure. This converts the initially harmful insoluble silver jarosite into a form that is soluble in cyanide leaching, thereby recovering the silver that would otherwise be lost.
Solution Approach 2:
The process introduces lime (calcium oxide or hydroxide) as an intermediary substance that mediates between the silver jarosite formed during pressure leaching and the cyanide leaching step. The lime boil treatment acts as an intermediate processing step that modifies the chemical structure of silver jarosite, making it susceptible to cyanide attack. This intermediary treatment resolves the contradiction by temporarily accepting jarosite formation then subsequently converting it to a cyanide-soluble form.
3Loss of substance
If lime boil process is used to break down silver jarosites, then silver solubility in cyanide leaching is improved, but copper and iron arsenate compounds break down forming unstable precipitates that may fail environmental stability tests
Solution Approach 1:
The process applies parameter changes by carefully controlling the Fe:As molar ratio to be greater than 4:1 and maintaining temperature above 200°C during pressure oxidative leaching. These parameter changes ensure that iron arsenate compounds form with high environmental stability (passing TCLP tests) while still allowing silver jarosite to form and subsequently be destroyed by lime boil. The specific parameter range optimizes both silver recovery and environmental stability simultaneously.
Solution Approach 2:
The process applies preliminary action by establishing the correct Fe:As ratio and temperature conditions before the lime boil step occurs. This preliminary control of leaching parameters ensures that when the lime boil subsequently destroys silver jarosite, the copper and iron precipitates that form have already been pre-conditioned to be environmentally stable. The preliminary Fe:As ratio control prevents formation of unstable copper arsenate compounds that would otherwise be created during lime boil.
4Loss of substance
If the Fe:As molar ratio is maintained at greater than 4:1 to limit copper arsenate precipitation, then copper recovery is improved, but the amount of arsenic that can be treated per unit autoclave volume is limited
Solution Approach 1:
The process resolves this contradiction through parameter changes by operating at elevated temperatures above 200°C during pressure oxidative leaching. This temperature parameter change increases the solubility and reaction kinetics, allowing the system to handle higher arsenic loads while maintaining the Fe:As ratio greater than 4:1. The high temperature enables more efficient copper dissolution and iron arsenate formation, increasing the autoclave's throughput capacity for arsenic-containing feeds.
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 enhances copper recovery while maintaining environmental stability, reduces operating costs by minimizing cyanide consumption, and allows for high silver recoveries without the need for intermediate jarosite destruction steps, thereby improving the overall efficiency and sustainability of the process.
Implementation Method 1
The sulphide components of the ore are at least partially oxidized to dissolve metal values into solution and to convert the sulphide sulphur to sulphate in solution
Implementation Method 2
pressure oxidative leaching involves subjecting a slurry including the ore or concentrate feed to elevated pressure and temperature in the presence of oxygen in a pressure vessel to decompose the minerals
Implementation Method 3
copper may precipitate as insoluble copper arsenate, resulting in insoluble losses of copper values to the pressure leach residue
Implementation Method 4
Gold typically remains as particles of metallic gold in pressure oxidative leaching, and, thus, is amenable to cyanide leaching
Data Source
AI summary
An integrated pressure leaching, heap leaching process for recovering copper from sulphidic feed containing iron, arsenic, and copper. Aqueous feed slurry of the sulphidic feed is pressure oxidized to form a liquid phase containing free sulphuric acid and aqueous copper sulphate, and to precipitate arsenic as solid iron arsenic compounds. Treated slurry is withdrawn from the pressure vessel and the liquid phase is separated from the solids. Copper is recovered from the separated liquid phase and generates a solution enriched in acid and depleted in copper. At least a portion of this solution is neutralized in a copper heap leach to produce a PLS containing copper and reduced in acid. At least a portion of the heap leach PLS is neutralized to produce a solution further reduced in acid, and solids containing copper precipitates, followed by a liquid solid separation. The solution further reduced in acid is recycled as process solution for the pressure leach, while the solids containing copper precipitates are recycled to combine with either the treated slurry from the pressure leach, or the liquid phase from liquid solid separation, to re-dissolve copper and other metal values. The solids from the latter step are separated and the liquid phase is fed to copper recovery.