Navigation

Arsenic Stabilisation

The occurrence of arsenic bearing minerals is increasing in base and precious metal deposits. Materials with elevated arsenic contents are difficult to process without the associated environmental risks. Due to limited alternatives, the arsenic is volatilized or left in tailings exposed to lixiviation. Very few facilities in the world are capable of treating material containing high levels of arsenic.

DST has developed a patented process for the sequestration and stabilization of the arsenic often associated with copper, gold, silver or polymetallic deposits. In DST’s novel and cost-effective approach, the arsenic is incorporated into a highly stable and insoluble glass form that can contain up to 20% arsenic, while meeting or exceeding the requirements of the United Stated Environmental Agency’s (EPA) toxicity characterization leaching procedure (TCLP, Method 1311) and the Synthetic Precipitation Leaching Procedure (“SPLP”).

Key feature

A key feature of DST’s process is that it allows for the stabilization of arsenic from a variety of sources such as:

  • Metallurgical flue dusts (smelting industry)
  • Mineral concentrates (arsenopyrite, cobaltite, enargite)
  • Arsenic contained in tailings
  • Arsenic from wastewaters or tailing drainages

Technology

The process allows vitrifying the arsenic by integrating it, under various forms, in a vitrification mixture of commonly available reagents, such as silica, recycled glass and hematite. The mixture is then vitrified producing a meta-stable oxide system of which can hold up to 20% arsenic, depending on the form or arsenic being vitrified.

Briquetting is used to control the dust from the mixed product going into the fusion furnace. The briquettes also help to keep the surface contacts between the arsenic product and ingredients, after mixing, to create a homogeneous glass product. The mixture and final glass composition will differ depending on the arsenic species entering the system. Depending on the arsenic form feed to the system some arsenic may volatize in the form of arsenic trioxide (As2O3) which can be recirculated in the system.

By using DST’s stabilization process, arsenical compounds can be successfully and permanently stabilized from their amorphous states providing greater process control latitude. The stability of glass offers a sequestration solution for arsenic that will hold over geological times, removing the need for waste disposal site monitoring ad infinitum.

Chart

DST’s Vitrification process circuit

Since the construction of its pilot plant in 2016, DST has successfully demonstrated its technology at the pilot level on arsenic trioxide flue dust wastes produced in a copper smelter operation. During the tests, DST reached optimal processing conditions for the successful vitrification of arsenical material. The program demonstrated the stability of the produced glass, containing up to 20.4% arsenic while exceeding the EPA’s TCLP guidelines.

DST’s arsenic vitrification program has continued to develop and reached the detailed engineering phase in 2017. DST is currently constructing its first industrial scale arsenic vitrification plant to be delivered onsite to a metals processing facility. The plant is designed to sequester up to 3,000 t/y of arsenical dusts. The construction of the plant will be completed in the third quarter of 2018, and after commissioning, will be operational in late 2018 or early 2019.

On September 2017, the State of Knowledge Review (“SOK”) was a report prepared by Arcadis Canada Inc. (“Arcadis”), on behalf of the Giant Mine Oversight Board ("GMOB"). The report concluded that arsenic vitrification was the best solution for permanent stabilization for the arsenical ducts currently buried in the Giant Mine. Arcadis’ mandate was to provide an assessment of technologies, methods, or integrated combinations of technologies and methods that are potentially relevant to the arsenic trioxide management at the Giant Mine site, north of Yellowknife in the Northwest Territories in Canada. Though a decision has not been made yet, the SOK will be used by the GMOB to help define research priorities for a permanent solution for the arsenic trioxide dust at Giant Mine that may be implemented in the future.

Arsenic Removal

DST has developed solutions for the removal of arsenic contained in mineral concentrates. The removal of arsenic, presented in the form of arsenopyrite or cobaltite, is done using a thermal decomposition in an inert environment in combination with stabilization of arsenic by vitrification. The arsenic content in the concentrate can be reduced by >95% , with no gold/cobalt losses, while retaining suitable sulphur contents for smelting operations.

This implies that concentrates can undergo an arsenic removal pre-treatment and output an arsenic depleted mineral concentrate acceptable for traditional base metal smelters without the penalties usually imposed to complex concentrates and a stable insoluble arsenical glass product.

DST currently displays its arsenical glass at its Montreal headquarters, where a salt water fish tank is lined with arsenical glass and the fish continue to thrive.