Alkaline Leaching of Refractory Ores Using Complexing Agents
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Solution Overview
Problem
Alkaline leaching methods for refractory ores result in lower precious metal recovery due to passivation by iron and arsenic compounds, requiring high pressures and temperatures, and are environmentally and economically unfavorable, while acidic leaching is more effective but not suitable for all ores.
Innovation Solution
A method involving milling mineral compositions to less than 25 µm, leaching with lime and/or limestone and a soluble alkali complexing agent in the presence of an oxygen-containing gas at a pH of 3.5 to 6, which forms soluble complexes that prevent passivation and enhance solubility, allowing for improved recovery of precious metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If alkaline leaching is used to process refractory ores, then operating costs and environmental impact are reduced by avoiding high pressure and temperature, but precious metal recovery is lowered due to passivation by iron and arsenic compounds
Solution Approach 1:
The patent changes the chemical parameters of alkaline leaching by introducing water-soluble alkali metal salts (NaOH, KOH, LiOH, RbOH, CsOH) and controlling pH levels to prevent passivation. This allows the process to operate under milder conditions while maintaining high precious metal recovery rates, resolving the contradiction between ease of manufacture and productivity.
Solution Approach 2:
The patent uses water-soluble alkali metal salts as intermediary substances that mediate between the ore and the leaching solution. These intermediaries prevent the formation of passive oxide and sulfur-rich layers by controlling the chemical environment, thereby enabling both mild operating conditions and high recovery rates simultaneously.
2Device complexity
If traditional cyanidation is used, then the process is simple and direct, but it cannot extract gold from refractory ores where gold is encapsulated within the ore
Solution Approach 1:
The patent applies preliminary oxidation treatment to refractory ores before cyanidation. This preliminary action liberates the encapsulated gold by oxidizing the surrounding mineral matrix, making the gold accessible to subsequent cyanide leaching. This two-stage approach maintains relative process simplicity while dramatically improving gold extraction efficiency from refractory ores.
3Productivity
If acid leaching is used to achieve high precious metal recovery, then recovery rates improve, but the method is unsuitable for ores requiring base metal recovery and has higher environmental impact
Solution Approach 1:
The patent changes the pH parameter of the leaching process by using water-soluble alkali metal salts to create and control alkaline conditions. This allows the process to achieve high precious metal recovery under alkaline conditions similar to acid leaching, while also being suitable for base metal recovery and having reduced environmental impact. The adaptable pH control enables the same process to handle different ore types effectively.
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 enhances the recovery of precious metals by preventing passivation and allowing for ambient pressure operation, reducing costs and environmental impact, while maintaining high recovery rates comparable to acidic leaching.
Implementation Method 1
leaching with lime and/or limestone and a soluble alkali complexing agent which forms soluble complexes that prevent passivation
Implementation Method 2
leaching said mineral composition in the presence of lime and/or limestone and a soluble alkali complexing agent at a pH in the range of from 3.5 to 6
Implementation Method 3
leaching the composition with a solution comprising lime and/or limestone in the presence of an oxygen containing gas
Implementation Method 4
milling the composition to a particle size of P80 of less than 25 μm
Data Source
AI summary
ABSTRACT A method for treating a mineral composition containing iron, arsenic or other Group VA compounds comprises milling the mineral composition to a particle size of P80 of less than 25 µm and leaching the mineral composition in the presence of lime and/or limestone and a soluble alkali complexing agent and in the presence of an oxygen containing gas at a pH in the range of from 3.5 to 6.