Crystallisation & Evaporation

A nickel refiner using the Sherritt Gordon process generated a dilute effluent which could be evaporated to produce ammonium sulfate crystals for sale and clean water for recycle. Conventional evaporative crystallisers produce fine crystals (0.7 mm diameter) that cannot be directly sold as fertiliser because they need to be combined into larger granules to meet the requirement of farmers. Oslo crystallisers can grow larger crystals but they can be tricky to start up and difficult to operate over long periods.

Jord’s Draft Tube Baffle (DTB) crystalliser has proved ideal for ammonium sulphate. Slurry is circulated and mixed in the draft tube. Unwanted fine crystals are separated in the baffle zone and then dissolved by circulating through a “fine destruction” heater. The larger crystals that remain can then be recovered.

Jord designed and built a DTB crystalliser for a nickel refiner in West Australia which produces crystals of more than 2 mm diameter. These are sold directly as fertiliser at premium prices. Evaporation is achieved at very low cost by using Mechanical Vapour Recompression (MVR) driven by a steam turbine. The turbine draws high pressure steam from the plant boiler and discharges into the low pressure distribution system.

This innovative project featured in multiple industry publications such as here on the front cover of Australian Mining.

A waste brine stream from the nickel roasters was fed to an evaporation pond. Jord used waste steam to evaporate 95% of this brine in forced circulation evaporators. The recovered steam was condensed in air cooled condensers, for re-cycle to the nickel smelter. Water recovery was the primary driver for this project. A thickened CaCl2 slurry was flaked and sold as a by-product.