Codelco required a sustainable, energy efficient Zero Liquid Discharge (ZLD) effluent treatment plant to process leach/cementation and SX effluent from their molybdenum processing facility. The stream contained arsenic and excess acid, which further complicated the treatment process.

We selected a two-stage approach for the design, supply, installation and commissioning of the effluent treatment. The first stage included a pre-treatment plant to remove metals and impurities (with specific emphasis on arsenic), generating a concentrated sodium chloride solution. The successful removal of iron and arsenic during the precipitation pre-treatment step – in the form of a filter cake with low leaching properties – was essential for safe disposal in an open landfill. We achieved this through oxidation using hydrogen peroxide and neutralisation with lime.

This was followed by a robust forced circulation crystalliser that’s able to handle variable feed composition, but primarily crystallising sodium chloride. The crystals are recovered using a screen bowl centrifuge from where they are discharged into a container as a damp crystal for disposal.

We also included two-stage mechanical vapour recompression fans (MVR), which resulted in a highly energy efficient crystalliser design. The crystalliser was provided in corrosion-resistant materials such as super duplex stainless steel, fibre reinforced plastic and titanium, in order to manage potential damage due to the aggressive high temperature chloride-containing liquors.

Within days of starting up, the plant successfully completed its performance tests. Codelco was able to recycle clean condensate with barely detectable traces of arsenic back to its process. The mixed salt was taken away at no cost to be used for de-icing roads in the high Andes.