Sodium Metabisulfite for Gold Precipitation Guide
By Pepetools - Precision Engineered Professional Equipment | Published: 2026-10-25
Category: How-to Guides
Learn how to use sodium metabisulfite to precipitate gold from aqua regia solution. Step-by-step guide for jewelers and refiners using Pepetools SMB.
Quick Answer
Sodium metabisulfite (SMB) is a reliable chemical for selectively precipitating gold from aqua regia solutions. Follow the steps below to safely and efficiently recover your gold.
Why Sodium Metabisulfite Works for Gold Precipitation
Sodium metabisulfite acts as a reducing agent, converting dissolved gold ions (Au³⁺) back into solid metallic gold. It is preferred over other reducers like ferrous sulfate because it is less messy, produces a purer precipitate, and works well in acidic aqua regia solutions. The reaction produces sulfur dioxide gas, so working in a fume hood or well-ventilated area is essential.
The Pepetools Sodium Metabisulfite is a high-purity technical-grade reducer specifically sourced for jewelry and refining applications. Its consistent quality helps minimize contamination and ensures reliable precipitation results.
How to Precipitate Gold with Sodium Metabisulfite
- Prepare Your Aqua Regia Solution: Ensure your gold-bearing solution is free of solids and has been properly diluted. The solution should be acidic (pH below 2) for SMB to work effectively. Slowly add the SMB powder while stirring gently. Common mistake: Adding SMB too quickly can cause violent foaming and overflow. Add in small increments.
- Observe the Precipitation Reaction: After adding SMB, the solution will turn brown and release sulfur dioxide gas. Gold will begin to settle as a dark brown or black powder at the bottom. Continue stirring occasionally and let the reaction complete for 30–60 minutes. Checkpoint: If no precipitate forms after 30 minutes, the solution may not be acidic enough. Add a few drops of hydrochloric acid to lower the pH.
- Filter and Wash the Gold: Use a fine filter paper or a vacuum filtration setup to collect the gold precipitate. Rinse the gold powder with distilled water, then with a small amount of ammonia to remove any residual silver or copper. Finally, rinse again with distilled water. Common mistake: Skipping the ammonia wash can leave trace metals that contaminate your final gold. Always perform at least one ammonia rinse.
- Dry and Melt the Gold: Transfer the washed gold powder to a clean crucible and dry it thoroughly under a heat lamp or in a low-temperature oven (200°F/93°C). Once dry, melt the gold with a torch or furnace. Add a small amount of borax as a flux to help the gold flow and collect impurities. Checkpoint: Ensure the gold is completely dry before melting; any moisture can cause spattering and loss of metal.
Product Facts
- Sodium Metabisulfite for Gold Precipitation: Premium Sodium Metabisulfite (SMB) is a high-potency technical-grade reducer sourced for selective precipitation of gold from aqua regia solutions. Using a consistent, high-purity SMB reduces the risk of introducing impurities that can discolor or weaken your recovered gold.
Sodium Metabisulfite for Gold Precipitation
