ZLD EVAPORATION CRYSTALLIZATION PLANT IN THE HYDROMETALLURGICAL INDUSTRY.

Environmental considerations along with economical benefits of the water re-use have triggered the interest of the industry to develop a new ZLD technology for the treatment of liquid effluents.

A hybrid ZLD process was developed for an effluent from a Molybdenum production facility of the Chilean company Molymet containing among others ammonium sulphate, sodium chloride, as well as magnesium and potassium sulphate. The process is foreseen for a waste water capacity of up to 110m3/h. The process consists of a pre-treatment section with brine purification, followed by a RO pre-concentration and further concentration in a falling film MVR evaporator. A crystallizer and a solid separation complete this process, which produces pure water for the re-use in the production facility under ZLD conditions. 

While existing technologies are rather sensitive to fouling and incrustation, the present process is specifically designed to remove the respective hardeners and fouling components in front of the concentrations units. The use of RO instead of evaporation allows a significant cost reduction and improves the overall process economics.

In order to proof the new process, laboratory and pilot tests were carried out, initially in the premises of the plant constructor and later on factory’s site at a larger scale. Major focus was on the full precipitation of the Calcium being the essential pre-condition for the economic use of the subsequently following concentration steps (membrane, evaporation, and crystallization), in the way that even the falling film evaporator could be operated un-seeded, thereby simplifying the overall process design. 

The process was tested successfully and showed excellent results. The critical compounds, i. e. fouling and incrustation forming components, like e.g. colloidal SiO2, Mn and Fe, could be reduced below any critical concentrations. 

Historically, Molymet has been a pioneer industry in caring for the environment. Since it foundation, the company consistently executes investments and countless actions designed to preserve and protect the environment, establishing concrete measures to going beyond the provisions made by the legislation.

The commissioning of the waste water plant at Molymet was a milestone in this respect. Involving a 20 million US$ investment. Since its installation the company won several awards with regards to their environmental policy.

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