As part of a series of blogs on jigs, in which we have taken a look at the development and relevance of the high recovery jigs, and the jig testing programme, this final blog will focus on the three most interesting applications of jigs. Here we offer you an insight into the actual use and operations of our jigs.

Alluvial mining: the origins of use for high recovery jigs

Royal IHC’s high recovery jigs were originally developed for application in typical alluvial or placer deposits containing valuable minerals like gold, tin, platinum and diamonds. In general, jigs are well suited to use in gold separation processes. This is due to the high specific density of gold which assures high efficiency in gravity separation, even for smaller particle size ranges. Gold tends to form tabular shaped particles, giving problems in the separation process when using thin flowing film concentrators. This makes the jig superior to other gravity methods, particularly for rougher duty/primary concentration. Because the jig is a thick bed separator, the particles are separated purely on density and not on shape or size. Allowing also the finest gold particles to be recovered.

Over time, high recovery jigs have been successfully applied in operations in different settings, collecting gold both on land and aboard integrated mining and processing dredgers. Nowadays, the opportunity for the high recovery jigs lies in legacy alluvial tailings, especially when thin bed separation methods were used before. Fine gold particles will be still present in the legacy tailings and  reprocessing with jigs can turn the perceived tailings into a valuable secondary resource. As tailings consist of already processed and often fine-grained material, it is ideally suited for the jigs. And it offers a safe and more sustainable rehabilitation solution for these deposits. 

Jigs as a pre-concentrator step: reducing energy consumption in grinding stage

With the mining industry taking a more focussed approach to sustainability, a key area is to look for ways to reduce a mine’s footprint. One of the options is to reduce total feed to the grinding stage of hard rock processing. Here, the application of a jig as a pre-concentrator step removes non mineralised material and thereby reduces the total feed to the ball mill circuit. As this is one of the most energy intensive stages in mineral processing, not having to mill the material before further processing, creates an enormous energy – and cost – saving. Next to that, it leaves tailings more coarse, creating less problems in final depositing of these tailings. 

So how does that work? You want a high recovery of the mineral(s) at an acceptable ratio of concentration in this pre-concentrator step. The most important requirement in obtaining this high recovery is the liberation degree of the wanted mineral(s). With our jigs and gravity as operating principle, we get a clear specific density distinction between the heavier (interesting) mineral and the lighter matrix material. Smaller sized crushing will give a higher liberation, however finer sized material is more difficult to separate by gravity and will add to the crushing costs.

Typically 1 or 2 stages of jigs are needed. Crushed material (usually up to 8 mm) is fed to the rougher stage, where a split is made between waste and concentrate. The waste is discarded as tailings, and the concentrate can be fed to a second jig stage, the cleaner stage. Here a similar efficiency can be achieved, increasing the ratio of concentration. The tailings are often recirculated to the rougher stage to improve recovery even more. The ultimate jig concentrate is then further treated.

In 2017 Royal IHC’s high recovery jigs were successfully applied as a pre-concentration step to concentrate Tungsten mineral (scheelite) from gangue​. By implementing the jigs in the processing plant, the client did not have to mill all the material before further processing, which gave them huge energy and cost savings. As a secondary benefit, a large portion of the tailings is separated out in the jig stages before milling and this results in coarser tailings, posing fewer issues during final depositing. 

Jigs as a pre-concentrator step in a processing plant
Jigs as a pre-concentrator step in a processing plant

Considering waste materials as an ore: Urban Mining and our jigs

Globally the focus on secondary resources, recycling and a circular economy has been increasing extensively over the last years. This is also strongly promoted by governments, and more waste materials are treated in order to recover valuable materials and metals for re-use. 

This drives the need for efficient and clean separation methods. The process should not harm the environment, be economical and generate high quality clean secondary resources. In the recycling industry gravity separation is often considered, as it involves materials with different densities and does not require chemical additives. This suits the jig’s capabilities perfectly!

Differences in material characteristics require changes in jig design, mostly related to shape and size of particles. But our high recovery jig has proven itself in waste materials. Royal IHC’s high recovery jigs have been part of two innovative projects in the Netherlands, one in a waste-to-energy plant and one in a bottom ash wash plant. In both cases, the goal was the same: to recover precious metals (gold, silver, platinum) and copper from bottom ash from incinerator waste. The tailings are used for (new) building materials. What started as pilot projects, are now mature operations. The high recovery jigs have been part of the full size plant and fully operational for several years now. 

Jig concentrate from bottom ash, with high content of valuable metals
Jig concentrate from bottom ash, with high content of valuable metals

As you can see, Royal IHC’s high recovery jigs can be used in different applications. Not only in the more obvious mineral processing situations, but also in industries you would probably not think of in first instance, such as recycling. All with the goal of making our clients’ activities more sustainable.

Written by 

Taco de Boer
Business Developer Mining & Mineral Processing