From the outset, the project aimed to design a fumehood that would meet the needs of the gold shops. Firstly, a steel fumehood was manufactured by students at a local technical school based on a water-trap concept provided by UNIDO. Secondly, a meeting of gold shop owners was held in the local administration office to discuss the relative merits and drawbacks of the prototype fumehood. Much practical information was derived from this exercise and furthermore, put to use in future designs.

Five technical students worked under supervision to build a prototype fumehood.

Initially, the fumehood was designed so that the crucible would sit above a gas flame inside an enclosed burning chamber. However, gold shop operators could not accept that the fumehood door had to be closed when burning, as they wanted to be able to watch over the process directly and handle the amalgam ball while burning it.

Thereafter, an attempt was made to introduce retorts as a solution for gold shops. This proved unsuccessful for the same reasons, plus the additional delay factor of a 20-minute turnaround time each time amalgam is burned in a retort. The project demonstrated kitchen-bowl retorts, pipe retorts, fish-tin retorts and a stainless steel ‘Fauzi’ retort.
The gold shop operators rejected the use of retorts but advocated their use in the field by miners for pre-burning amalgam. However, one gold shop reported using a ‘Fauzi’ retort on an occasional basis when substantial amounts of amalgam had been accumulated.

The prototype fumehood then went through several experimental metamorphoses:

First of all, a pipe retort was fixed inside the burning chamber; although this worked as both a retort and as a fumehood that prevented any fumes from escaping, it required too much time and energy to be a successful solution for gold shop operators.

A pipe retort fitted into the fumehood proved unrealistically slow to this gold shop operator.

Secondly, the blower was relocated and placed after the water trap, otherwise mercury would accumulate inside it. It could then no longer blow contaminated gas into the water but instead had to suck the gas through a cooling box where condensation could occur.

Thirdly; the water box was filled with glass marbles and pebbles to create a larger surface area for the fumes to adhere to. Although this worked, it created a high level of resistance – the airflow was positive and fumes were sucked into the trap, yet some still escaped from the front of the chamber when the mercury combusted. This was primarily due to having insufficient volume to accommodate the gas inside the burning chamber.

Glass marbles facilitate condensation of mercury fumes inside a water trap.

Finally, a return was made to the original concept which worked solely as a water trap. A second fumehood was then built from stainless steel which incorporated a water tray throughout the base of the unit for cooling and collection of mercury. These prototype fumehoods became a part of the transportable demonstration unit’s equipment.

Towards the end of the campaign, it was decided to implement a program of direct intervention in gold shops. Having experimented with filtration systems using water-boxes some of the problems with resistance to air flow had been resolved. Therefore, the project was able to provide technical assistance, equipment and expertise to fifteen gold shops--out of a total of 35--that expressed a wish to modify their existing chimneys. These interventions were successful, and continue to demonstrate to other gold shops that the recapture of high levels of mercury for recycling and resale is easily obtainable.

Recycled mercury captured by the modified fumehood in the background.

This was only possible because the project sought the participation of gold shop owners from the outset and was therefore able to have close consultation with them by the end of the program, as mutual trust and rapport had been established. These fifteen gold shops were willing to display posters in their shops and share detailed information about the quantities of gold and amalgam that they traded. As a result, the quantity of amalgam each shop burned annually was established. From this study, it was determined that the 35 gold shops in the town combusted and released 1.5 tonnes of mercury during 2006.