The most common way of separating gold amalgam from mercury is through burning or roasting to free excess mercury. The question, however, is how can miners manage this practice best?
Due to the danger that mercury vapour poses to human bodies, it is vital that miners handle the element carefully. Artisanal and small-scale gold miners should distil mercury in a closed retort when working with amalgam. Not only will it ensure the safety of the miners and the environment, but it will also help recycle the mercury. In a closed mercury retort, amalgam heats within the sealed chamber thereby allowing mercury to evaporate and eventually condense for reuse.
A mercury retort is a small device designed to burn amalgam safely without losing the mercury vapour in the air. This device also reduces air pollution and the miners’ harmful exposure to mercury.
Project Inception: The Impact Facility, MAKAL and Maxius Engineering.
The Impact Facility (TIF) in collaboration with MAKAL, a downstream actor in ethical jewellery production, supported the fabrication and installation of eight retorts and burning systems at a Kenyan fabrication company. The partners intend to train miners on the use of these facilities in their line of work. This project provides miners with the opportunity to learn of, and reduce contact with, the harmful effects of the mercury fumes.
TIF identified Maxius Engineering Limited (MEL) as a suitable service provider in fabricating mining equipment, with the latter’s personnel comprising of mining and mechanical engineers. After delivering a professional retort design to Eng. Dadson Mwangi (MEL) for review, the latter commenced the fabrication process, with the model you see in the video below.
Blueprint for Mercury Retort Fabrication
The following components are required to fabricate a mercury retort,
- A 4ft stainless pipe worth ½ inch in diameter.
- Mild steel water pipe worth 1 1/2-inch in diameter.
- A reducer (1½” in diameter) and a socket (13/4” diameter), all stainless-steel.
- One reducing bush connector.
- Round steel rods (1/4-inch diameter) to create the stand.
Equipment Needed for Fabrication
- Welding Machine
- Cutting/Grinding machine.
- Gas welding
- Tig machine to weld stainless steel with galvanized steel.
- Engineering Anvil and Vice.
The steps to create a retort
1. Bend the stainless-steel pipe to make a smooth curve at one end of the tube before cutting it.
2. Join the bent end with the reducer through the reducing bush connector. This end creates a point where amalgam is placed inside the plug and closed to the reducer by a thread.
3. Cut a mild steep tube, 250mm long, and seal the hollow end with circular plates through welding.
4. Make circular holes (½ inch in diameter) at the centre of each end of the sealed steel tube. A professional welder can make a hole with a normal welding flame or gas welding.
5. Drill two more holes (using either a metal drill or gas welding) along the surface of the steel tube such that they are both positioned 11/2 inches from each end, and on the same line.
6. You can now insert the free end of the stainless steel pipe to the first hole in the cooling section of mild stainless steel, pass the end across until it exits at the other side such that the reducer is left hanging mid-air.
7. You can now weld the joint between the steel tube (the one meant to cool the mercury vapour) and the entry point of the stainless-steel pipe, making sure to leave a portion of it hanging 150 mm long on the reducer end.
8. Cut and fold the steel rod to make a triangle shape 300mm high (from top to bottom) and another at 250mm.
9. Now with your steel tube inside the stainless steel system (or cooling section) and reducer on one end, weld the triangular support steel rod’s most extended tip (the 300mm shape) on one end of the steel tube (the area closer to the reducer section).
10. Weld the other triangular rod shape (the 250mm one) at the other end of the steel tube (towards the mercury collection point) so that it forms a base and supports itself. Set both triangles at a gradient.
11. Cut the excess stainless steel, slightly off the cooling section of the retort, to allow the mercury liquid to flow in a small container which will be placed underneath the exit point.
12. Paint the mild steel tube thoroughly to guard against rust and proceed to use your retort.
Important Points to Note About the Materials Used in Retort Fabrication
- The burning area shown as 4 and 9 is the area where the Gold amalgam is inserted for burning. Part 1, 2 and 3 are plumbing parts which close each other using threads. They are also made up of stainless steel so that the burning amalgam does not react with the metal parts.
- The stainless-steel tube part 1, which runs from the end of the reducer to the other, ensures that mercury vapour and later liquid travel along the pipe without reacting with the metal surface.
- The Steel tube enclosing the stainless-steel tube part 2 is also known as the water jacket where water circulates, thus cooling mercury vapour travelling along the stainless-steel tube.
- The two nipple-points shown as no. 7, help to connect a water pipe for water to travel from the lower end to the higher end of the water jacket cooling off the system, and the mercury fumes into liquid form.