Zero Liquid Discharge plant for molybdenum processing facility in Chile.
Molyb required a sustainable, energy efficient Zero Liquid Discharge (ZLD) effluent treatment plant to process a leach/cementation and SX effluent from their molybdenum processing facility. The stream contained arsenic and excess acid, which further complicated the treatment process.
PROXA selected a 2-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. 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.
HOW PROXA ADDED VALUE
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. We also included 2 stage mechanical vapour recompression fans (MVR), which resulted in a highly energy efficient crystalliser design. And, given our extensive experience in crystallisation, we also provided the crystalliser 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. What’s more, our design ensured that the collected clean process condensate is not contaminated by carry-over salts and can be reused on the site.
Leach/cementation and SX effluents
- Mixed salts for disposal
- Clean condensate for reuse
- Calcium carbonate cake for disposal (or reuse within the plant)
- 14,4 m3/hr effluent
- 12 500 kg/hr evaporation
- 33.6 tons/day mixed salts
- Filter press
- Forced circulation crystallisation
The plant has been in continuous operation since September 2016 and is meeting all client’s key performance objectives.