Urban Mining 101: Recovering Gold from PCBs with Nitric Acid
Did you know that one ton of circuit boards contains 40–800 times more gold than one ton of gold ore? Old computers, smartphones, servers, and electronics are a genuine source of recoverable precious metals — and nitric acid is the primary chemical tool used to extract them.
This is called urban mining: recovering valuable metals from electronic waste (e-waste) rather than virgin ore. It’s practiced by hobbyists, small refiners, and large-scale recyclers worldwide. Here’s how it works.
Where Is the Gold in Electronics?
Gold is used in electronics because it’s an excellent conductor and highly resistant to corrosion. You’ll find it concentrated in:
- CPU processors — gold-plated pins and internal connections; among the richest sources
- RAM sticks — gold edge connectors
- Motherboards — gold-plated connectors, slots, and traces
- PCI cards & expansion cards — gold fingers on edge connectors
- Hard drive platters & heads — small but present
- Smartphones & tablets — gold bonding wires in chips and connectors
- Telecommunications equipment — often higher gold content than consumer electronics
The gold-plated “fingers” on RAM and PCI cards are the easiest starting point for beginners — they’re easy to identify, easy to strip, and yield relatively consistent results.
Two Main Methods: Nitric Acid Stripping vs. Aqua Regia
Method 1: Nitric Acid Stripping (Selective Dissolution)
Nitric acid dissolves base metals (copper, nickel, tin) but does not dissolve gold. This makes it useful for selectively stripping base metals away from gold-plated surfaces, leaving behind gold flakes or foils.
Process overview:
- Remove gold fingers or gold-plated components from the PCB
- Place in a glass beaker with 67% nitric acid in a fume hood
- The acid dissolves copper, nickel, and other base metals; gold remains undissolved
- Filter the solution — gold flakes are captured on the filter paper
- Wash, dry, and melt the gold flakes into a button or bar
Best for: Gold fingers, edge connectors, and gold-plated contacts where the gold layer is physically separable from the substrate.
Method 2: Aqua Regia (Full Dissolution & Precipitation)
Aqua regia (1 part nitric acid + 3 parts hydrochloric acid) dissolves gold completely into solution, then a reducing agent precipitates it back out as pure gold powder. This method recovers gold from more complex sources where physical separation isn’t practical.
Best for: CPUs, chips, and materials where gold is bonded or alloyed with other metals that can’t be easily separated first.
See our full Aqua Regia Gold Refining Guide for the complete step-by-step process.
Step-by-Step: Nitric Acid PCB Gold Stripping
What You’ll Need
- Nitric Acid 67% Lab Grade
- Borosilicate glass beakers
- Glass stirring rod
- Filter paper and funnel
- Fume hood or outdoor workspace
- Full PPE: acid-resistant gloves, splash goggles, face shield, acid-resistant apron, respirator
- Distilled water for washing
- Crucible and torch for melting (optional)
The Process
- Prepare your material: Remove gold fingers from PCBs. Cut or shear them into smaller pieces if needed. Remove any plastic or non-metallic components.
- Set up your workspace: Work in a fume hood or outdoors. Nitric acid produces toxic NO₂ fumes — ventilation is non-negotiable.
- Add material to acid: Place PCB fingers in a glass beaker. Add enough 67% nitric acid to submerge the material. The acid will begin dissolving base metals immediately, turning blue-green (copper nitrate in solution).
- Wait for dissolution: Allow the reaction to complete — typically 30 minutes to several hours depending on material volume. Gentle warming speeds the process but increases fuming.
- Filter: Pour the solution through filter paper. Gold flakes and foils are captured; the blue-green copper nitrate solution passes through.
- Wash the gold: Rinse the gold on the filter paper with distilled water several times to remove residual acid.
- Dry and melt: Allow to dry completely, then melt in a crucible to form a gold button. Weigh and assay to determine purity.
What to Expect: Realistic Yields
Urban mining yields vary significantly by source material:
- RAM gold fingers: Approximately 0.5–1g of gold per pound of fingers
- CPU processors (older Intel/AMD): 0.1–0.3g per processor
- Motherboards (general): 0.5–1.5g per pound
- Telecom equipment: Can be significantly higher — often 3–5x consumer electronics
Profitability depends on your source material cost, chemical costs, and gold price. Many hobbyists do this for the chemistry and satisfaction of recovery rather than pure profit — though with the right feedstock, it can be economically viable.
Safety Reminders
- Always work with full PPE — nitric acid causes severe burns on contact
- Never work in an enclosed space without fume extraction
- Dispose of spent acid solution (copper nitrate waste) as hazardous waste — neutralize with baking soda first
- Keep a baking soda solution nearby for spill neutralization
Get Started with Lab-Grade Nitric Acid
Grow It Depot stocks Nitric Acid 67% Lab Grade — the standard concentration for PCB gold recovery and aqua regia refining. Available from quart to 55-gallon drum, shipped in DOT-compliant FLPE bottles with a Certificate of Analysis.
⭐ Best value: The 4x Quarts bundle ships without a hazmat fee — ideal for hobbyists and small-scale refiners.