Acidless Separation

The Acidless Separation® machine is also quick and easy to use. It is a fully automatic process and is based on three operations, resulting in a reduction in labour and production costs. This is due to lower energy consumption and also the fact that not only are the precious metal recovery times considerably shorter, but there is also a saving on the costs of managing hazardous materials, which are not required by the ALS process. This process is also safer for staff and the environment, as well as generating a high yield and a rapid return on investment.

History of the collaboration agreement

In 2013, a meeting between IKOI and EZ-OCM gave rise to the idea of developing, patenting and marketing the ALS technology, starting from the technology that had already been in use in the EZ-OCM plants since the 1990s.

This idea originated from the fact that all the refining methods adopted across the world require the use of hazardous materials. The difference and advantage of the new process over the more established processes is that the process is based on the different degrees of volatility of the materials and therefore requires no chemical additives such as acids or other hazardous materials. Instead the ALS process separates the metals through sublimation of the more volatile metals (e.g. silver, zinc, lead and selenium), and thus allows these metals to be separated from the alloy through distillation and captured in a water-cooled collector. EZ-OCM has used equipment based on these physical principles since the early 1990s. In 2013, EZ-OCM found the collaborator suitable for developing this technology. IKOI is one of the industry leaders in terms of the research and development of innovative technologies for the heat treatment of precious metals. The collaboration agreement is based on the fact that EZ-OCM manages the raw materials for the tests and analyses the results of the tests, while IKOI undertakes the research and development, design and construction of plants, marketing, sales and after-sales service.

Table 1: Composition of the two alloys of the first two series of tests

Research & development

Over the past two years, IKOI, with the collaboration of EZ-OCM, has designed and produced some ALS machines. The first step for IKOI was to study and analyse the correlation between the pressure and temperature necessary for the sublimation of the materials. Once IKOI had determined the temperatures and degrees of vacuum that were necessary for the machine, the company began to design the first prototype based in part on the machine already in use in the EZ-OCM plants.

A typical ALS plant consists of:

• A vacuum chamber with a maximum degree of vacuum of ~1x10-4 mbar;
• An overpressure of nitrogen or argon for the purging and rapid cooling of the hot parts;
• Two vacuum pumps, one two-stage rotary vane pump and one Roots pump;
• A touchscreen synoptic display equipped with software for managing and controlling all the parameters;
• An IGBT power generator;
• Two condensers (this technology is protected by a global patent): one for the more volatile materials and the other for silver, which is used to collect evaporated metals;
• One melting head.

The first series of tests was carried out at IKOI with a copper-silver alloy used for the similar vapour tension between copper and gold, as can be seen in Chart 1 above. Other tests were carried out with a three-component alloy using two condensers. This series of tests was carried out to check the movement of the crucible from the first condenser for the more volatile materials (such as zinc, lead and selenium) to the second condenser for the materials with an average degree of volatility (such as silver), while the less volatile materials (such as gold) remained inside the crucible.

When the Research and Development team at IKOI decided that the machine was ready to operate with a real gold alloy, IKOI sent the prototype to EZ-OCM, as stipulated in the collaboration agreement and, at this point, another series of tests began at its plants. These tests, which were followed by the Research and Development team at IKOI, identified the improvements to the machine that were necessary to make the operations per formed at a refinery easier for the staff to undertake.

Results of the tests

We shall now explain the results of the first two series of tests. The first series of tests was carried out using one condenser only, while the second series of tests was carried out using two condensers.

The table below (see Table 1) shows the average initial composition of the gold alloys used for the two series of tests. After a few tests with the ALS technology, the results of the first series of tests (average values) only presented ~3% of silver in the block of gold that remained in the crucible, while the sublimated silver contained ~3% of gold.

The second series of tests using the ALS machine on a complex gold alloy gave surprising results:

• All the impurities (zinc, selenium and lead) in the first condenser were sublimated;
• The second condenser contained ~96.5% of silver and only ~2% of gold;
• The block that remained in the crucible had a purity of about 90% of gold, with ~5% of copper and another ~5% of silver.

Chart 2 above is based on the second series of tests, the one with numerous impurities in the gold alloy. Chart 2a illustrates the correlation between time, the temperature of the crucible, the temperature of the diversion devices on the condenser units and the pressure inside the vacuum chamber. The condenser is changed at the height of the red line (see Chart 2 above) and, as the pressure decreases, the temperature of the first cluster diversion devices decreases and, at the same time, the second diversion device warms up as the temperature in the crucible increases. The zinc, selenium and lead are made to sublimate at a high pressure simply by increasing the temperature. After the transfer from the first to the second condenser, the pressure decreases in order to make the silver sublimate and to capture it in the second condenser.

Figure 4b shows the decrease in weight of the material inside the crucible, and the variation due to the sublimation of the silver is measured using a load cell. The transfer from the first to the second condenser is automatic and is set by the operator at the start of the process. This happens when the more volatile materials have sublimated completely and have been captured in the first condenser. The operator will know when this happens on the basis of the initial composition of the gold alloy and its initial weight.

Figure 5 shows some examples of gold alloy and the results obtained following the Acidless Separation® process. Figure 5a shows the billet of the six-component gold alloy that was input and treated during the second series of tests; figure 5b depicts the materials (zinc, selenium and lead) captured in the first condenser; figure 5c illustrates the silver which is captured in the second condenser (purity of about 98%) and figure 5d shows the block of gold and copper that remained inside the crucible.