LLC “Scientific – Research Center “Gidrometallurgiya”, Saint Petersburg, Russia:

Ya. M. Shneerson, CEO, e-mail: src@gidrometall.ru
L. V. Chugaev, Principal Researcher

In 2008 Petropavlovsk Group established a research centre Gidrometallurgiya. The priority task of the Centre was to develop an autoclave process for double refractory carbon flotation concentrates produced from the Malomyr (M) and Pioner (P) ores. The Centre had state-of-the-art laboratory equipment. A pilot autoclave unit was built in the company’s testing facility in Blagoveshchensk, Amur Region, which was then used for testing various pressure oxidation regimes. A comprehensive study of the autoclave preg-robbing process was carried out. It was established that the most typical features of preg-robbing included high sensitivity to the concentration of organic carbon in the concentrate and the presence of chloride ions in the autoclave solution. It was found that the effect of preg-robbing manifests itself at the final stages of the process when the sulphide oxidation process is at its final stage, and the slurry ORP is getting close to 520–530 mV (silver-chloride electrode scale) and exceeding those values. It is in this phase (in the overoxidation phase) that the negative effect of organic carbon in the concentrate and that of chloride in the solution are most pronounced. A new technique was developed for quantitative evaluation of oxidized gold in refractory sulphide concentrates. With the help of this technique the authors established that oxidized gold was present in many concentrates and in some of them it is the dominant form. This technique can help streamline the extraction of gold from refractory ores and concentrates. It can also help understand the conditions, mechanism and trends behind the formation of gold containing sulphide ores. It is shown that autoclave preg-robbing is not applicable to all the gold present
in a material but to its oxidized part. The latter appears to be more reactive than Au0 and can open up as the result of sulphide oxidation. When a material contains a lot of oxidized gold, it can be described as a triple refractory material. The authors tested various methods for preventing autoclave preg-robbing. The most effective and practicable methods include a reduced concentration of organic carbon in the flotation concentrate (as low as 0.5–0.6%), a strict control over the concentration of Cl^– in the autoclave solution (no higher than 7 mg/l) and a limited feed of oxygen in the autoclave unit (to avoid overoxidation). The pilot POX testing of a few samples of the M concentrate showed that the above conditions would ensure a minimum of 91–93% recovery of gold. The pilot test unit was used to test various pressure oxidation regimes on the M and P concentrates, including the concentrates with non-standard concentrations of sulphur and carbon. The developed process proved to be reliable. The effort taken by the Gidrometallurgiya research centre resulted in the creation of a technique for processing refractory gold concentrates produced from the Malomyr and Pioner ores. Following the research study conducted, Outotec came up with a basic (2011) and later a detailed design (2013) for the Pokrovsk Hydrometallurgical Complex, which was put into operation in December 2018.

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