Bioleaching Precious Metals from Fly Ash Using Heterotrophic Microorganisms
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Solution Overview
Problem
Current biomining processes for recovering precious metals from secondary sources like fly ashes and e-scrap are inefficient, particularly for metals like gold and silver, as they are insoluble in sulfuric acid and require high-cost nutrients, media, and energy, and are not economically viable for low-value materials with trace metal contents.
Innovation Solution
A process involving sieving to obtain fractions with particle diameters between 0.1 and 0.2 mm, followed by a bioleaching step using heterotrophic microorganisms like Bacillus megaterium and Pseudomonas species, which selectively enrich precious metals while depleting unwanted metals like lead and copper, enhancing the recovery efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional biomining processes using autotrophic bacteria are used to recover precious metals, then copper recovery is achieved through sulfuric acid production, but precious metals like gold and silver remain insoluble and unrecoverable
Solution Approach 1:
The patent changes the pH parameter from acidic (conventional biomining) to alkaline conditions (pH 9-11), enabling precious metal solubility. It also changes the microorganism type from autotrophic to heterotrophic, and changes the carbon source from carbon dioxide to organic carbon sources like molasses or glucose, creating conditions where precious metals become soluble and recoverable
Solution Approach 2:
The patent introduces heterotrophic microorganisms as intermediaries that produce different metabolic byproducts compared to autotrophic bacteria. These heterotrophic microorganisms generate alkaline conditions and specific chemical environments that enable precious metal dissolution, acting as a mediator between the waste material and metal recovery
2Productivity
If bioleaching processes are optimized for copper recovery using autotrophic bacteria, then copper forms soluble sulfate, but the process runs slowly and does not work for precious metals
Solution Approach 1:
The patent fundamentally changes multiple parameters: pH from acidic to alkaline (9-11), microorganism type from autotrophic to heterotrophic, and carbon source from inorganic (CO2) to organic (molasses, glucose). These parameter changes transform the bioleaching process to be effective for precious metals while maintaining productivity
Solution Approach 2:
Instead of following the conventional approach of using acidic conditions and autotrophic bacteria for metal leaching, the patent inverts the approach by using alkaline conditions and heterotrophic microorganisms. This inversion creates a process that is effective for precious metals rather than just copper
3Quantity of substance
If high-cost nutrients and media components are used in bioleaching processes, then microorganism growth is supported, but the process becomes economically unviable for low-value materials with trace metal contents
Solution Approach 1:
The patent replaces expensive, complex nutrients and media components with cheap, readily available organic materials like molasses or glucose as carbon sources. These inexpensive substrates support heterotrophic microorganism growth effectively, making the process economically viable for treating low-value waste materials with trace metal contents
Solution Approach 2:
The heterotrophic microorganisms can utilize simple organic carbon sources that are already present in many waste streams or can be added as inexpensive byproducts. The system essentially feeds itself using cheap carbon sources, reducing the need for expensive specialized nutrients and media
4Quantity of substance
If waste materials with trace metal contents are treated using conventional bioleaching, then the process is designed for rich metal materials, but it becomes economically unviable for low-value materials
Solution Approach 1:
The patent changes the operational parameters to alkaline pH (9-11) and uses heterotrophic microorganisms with organic carbon sources, creating conditions that enhance metal solubility and recovery efficiency. These parameter changes make the process effective and economical even for waste materials with only trace metal contents
Solution Approach 2:
By using inexpensive carbon sources like molasses or glucose instead of costly nutrients, the patent makes the treatment of low-value waste materials economically viable. The cheap substrate supports sufficient microorganism growth to extract trace metals profitably
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 significantly increases the content of precious metals in the targeted fraction, improves recovery rates through bioleaching, and reduces the amount of unwanted metals, providing a more economically viable and environmentally friendly method for metal recovery.
Implementation Method 1
subjecting the fraction obtained in step (b) to a bioleaching process capable of recovering said precious metals from the waste residue, wherein heterotrophic microorganisms are used which are selected from the group consisting of Bacillus megaterium, Bacillus mycoides, Chromobacterium aquaticum, Pseudomonas species, Pseudomonas BR11571, Rhodococcus species, Stenothrophomonas species and Streptomyces species
Implementation Method 2
The processes involve a bioleaching step preferably using algae or blue-green cyanobacteriae as suitable microorganisms for producing and releasing hydrocyanic acid to form gold complexes
Data Source
AI summary
Suggested is a process for recovering precious metals from secondary sources encompassing the following steps: (a) providing a secondary source selected from the group consisting of flow ashes, incineration ashes or their concentrates; (b) subjecting said source of step (a) to a sieving process to obtain a fraction comprising particles having a diameter ranging from about 0.05 to about 1 mm; and (c) subjecting the fraction obtained in step (b) to any process capable of recovering said precious metals from the waste residue