How to extract gold from e-waste

Summary of advanced methods and technologies for extracting gold from electronic waste
Extracting gold from electronic waste (such as waste circuit boards, mobile phones, and computers) requires a combination of multidisciplinary technologies such as chemistry, biology, and physics. The following are the current mainstream methods and cutting-edge technologies, covering high efficiency, environmental protection, and economic considerations:

I. Chemical adsorption method

1. New composite material adsorption
   MoS₂-TpTa composite material: The adsorption capacity of gold is significantly improved by combining a covalent organic framework (COF) with molybdenum disulfide (MoS₂). The material has an adsorption capacity of up to 2564.80 mg/g at pH 5, and can selectively recover gold from actual circuit board leachate with a recovery rate of more than 90%3.

Advantages: High selectivity, strong chemical stability, and suitable for complex wastewater environments.

2. Polymer adsorption (such as porphyrin-based polymers)
   The porphyrin-based porous polymer developed by the Korean team can capture gold atoms 10 times its volume in a single hole through ultraviolet-assisted electron transfer. After acid leaching, the gold recovery rate reached 94%, and the polymer can be reused, with significant cost-effectiveness (1 gram of polymer can recover gold worth $64.

Application scenario: suitable for small-scale recycling, with a cost as low as $5/gram of polymer, suitable for developing countries.

II. Bioextraction method

1. Microbial adsorption and biometallurgy
   Bacterial adsorption: New Zealand company Mint Innovation uses specific bacteria (such as sulfur oxidizing bacteria) to selectively adsorb gold, and treats waste circuit boards through electrolysis and bioreactors, recovering 0.5 tons of gold and 800 tons of copper annually. The process has low energy consumption and no toxic byproducts6.

Protein separation technology: The Pennsylvania State University team used lanmodulin protein in plant bacteria and combined it with resin microbead columns to selectively adsorb rare earth elements (such as neodymium), which may be expanded to gold recovery6 in the future.

2. Enzyme catalysis method
   Some studies use enzyme catalysis to decompose metal bonds in electronic waste, but the technology is still in the experimental stage and the efficiency needs to be improved.

III. Traditional hydrometallurgy

1. Cyanide leaching
   Principle: Use sodium cyanide solution to dissolve gold to generate gold cyanide complex, and then recover it through zinc powder replacement or activated carbon adsorption.

Disadvantages: Highly toxic chemicals need to be strictly controlled, wastewater treatment costs are high, and it is easy to cause environmental pollution.

2. Thiosulfate leaching
   Alternative solution: Replace cyanide with thiosulfate, which has lower toxicity and high tolerance to impurities such as copper, but requires copper or ammonia catalysis, and the process stability needs to be optimized.

IV. Pyrometallurgy and electrolysis

1. High-temperature smelting
   Large smelters separate metals by melting electronic waste, and the gold recovery rate can reach more than 95%, but the energy consumption is high (requires more than 1200°C) and emits toxic gases such as dioxins.
2. Electrolytic gold removal
   The gold-plated parts are dissolved by electrolyte (such as thiourea system), and the gold is deposited on the cathode in the form of pure metal. The recovery rate is 97%-98%, which is suitable for large-scale production.

V. Comparison of key technologies and economic performance
Method Recovery rate Environmental protection Cost Applicable scenarios
Chemical adsorption method 90%-95% High Medium-low Complex wastewater, high selectivity requirements
Biological extraction 80%-90% Very high Low Green recycling, small and medium scale
Cyanide leaching 95%-98% Low High Industrial mature process
Pyrometallurgy 95%+ Very low Very high Large-scale centralized processing
Six, environmental protection and safety considerations
Toxic substance control: E-waste contains heavy metals such as lead, mercury, and cadmium. Illegal incineration or acid leaching will release carcinogens (such as dioxins), requiring professional protection and wastewater treatment systems.

Regulatory compliance: Follow the Basel Convention and the e-waste management regulations of various countries (such as India’s “Electronic Waste Management Rules 2022”) to avoid illegal cross-border transfer.

Circular economy: The global annual output of e-waste exceeds 62 million tons, and only 17.4% is formally recycled. Efficient extraction technology can reduce mining demand and reduce 5.2 billion tons of carbon emissions.

Seven, future trends
Green chemical technology: Develop cyanide-free leaching agents and biosorbents to reduce chemical pollution.

Modular recycling equipment: such as Mint Innovation’s urban biorefinery, localized processing and reduced transportation costs.

Precious metal “urban mine”: 1 ton of used mobile phones contains 10 times more gold than gold mines, with an economic potential of US$57 billion, which promotes companies to layout circular supply chains.

Summary
Gold extraction requires a balance between efficiency, cost and environmental protection. Chemical adsorption and biological extraction have become research hotspots due to their green and high efficiency, while traditional wet and fire methods still dominate industrial applications. In the future, technology will develop in the direction of low toxicity, high selectivity, and modularization, helping electronic waste to transform from an “environmental burden” to a “resource treasure house.”