Oxidative Bioleaching Pretreatment for Faster Base Metal Recovery
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Solution Overview
Problem
Existing bioleaching processes for base metals, particularly copper and nickel sulfides and oxides, are hindered by the inhibitory effects of nitrate and nitrite compounds on microbial growth, leading to inefficient leaching rates and prolonged cycle times.
Innovation Solution
A pre-treatment process involving ore agglomeration with an acidic sulfate solution containing optimized quantities of nitrate or nitrite creates a highly oxidizing environment, accelerating sulfide mineral oxidation and leaching rates through a series of steps including agglomeration, curing, and bioleaching, while separating nitrate/nitrite use from microbial inoculation to avoid inhibition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nitrate or nitrite compounds are added to enhance oxidation potential and accelerate leaching rates, then the leaching rate improves, but microbial growth is inhibited
Solution Approach 1:
The patent applies preliminary action by adding nitrate or nitrite compounds during the agglomeration and curing steps before microbial inoculation. This allows the ore to be pre-oxidized and prepared in advance, creating a more reactive material that will leach faster when microbes are introduced, without exposing the microbes to inhibitory nitrate/nitrite concentrations during their growth phase
Solution Approach 2:
The patent segments the leaching process into distinct phases: agglomeration with nitrate/nitrite addition, curing, microbial inoculation, and bioleaching. This temporal and functional segmentation allows nitrate/nitrite to be used effectively for oxidation during agglomeration and curing, while microbes are introduced separately during inoculation when nitrate/nitrite levels are reduced or absent, thus avoiding microbial inhibition
2Productivity
If fine milling of ore is performed to increase surface area and improve leaching efficiency, then copper dissolution increases, but processing complexity and cost increase
Solution Approach 1:
The patent changes the chemical parameters of the leaching environment by adding nitrate or nitrite compounds, which significantly enhance the oxidation potential and reactivity toward sulfide minerals. This chemical parameter change allows coarser ore particles to leach more efficiently, reducing the need for extensive fine milling and associated processing complexity
3Productivity
If temperature is increased to accelerate reaction rates and improve copper recovery, then leaching efficiency improves, but energy consumption increases
Solution Approach 1:
The patent employs strong oxidants (nitrate or nitrite compounds) that dramatically accelerate the oxidation of sulfide minerals at lower temperatures. This chemical acceleration allows effective leaching to occur at moderate temperatures, reducing the need for high-temperature processing and associated energy consumption while maintaining high copper 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
This approach enhances leaching rates and reduces cycle times by maintaining high oxidation potentials and microbial activity, effectively recovering base metals like copper and nickel with improved efficiency and reduced operational costs.
Implementation Method 1
The oxidative action of nitrate and nitrite in aqueous solutions of sulfuric acid is extensively described in the literature and patent prior art
Implementation Method 2
The nitrate/nitrite ions act as direct oxygen atom donors, rather than as electron acceptors
Implementation Method 3
an inoculation step and a leach step to bioleach a base metal from the ore
Data Source
AI summary
An oxidative bioleaching process for leaching a base metal from an ore that includes an ore agglomeration step, an ore stacking step wherein agglomerated ore is stacked to form a heap, a curing step, a rinse step, an inoculation step and a leach step, and wherein, during the ore agglomeration step, the ore is contacted with an acid solution containing nitrate or nitrite thereby to accelerate the leaching rate in the leach step.