Process Plant Technology (Pty) Ltd
Zero Liquid Discharge (ZLD) Plants
Increasingly, legislation and industry demands that no liquid effluents are to be discharged either into a river or storage (evaporation) dam but rather that a zero liquid discharge (ZLD) process be implemented generating solid products which can either be sold or more acceptably stored in a sealed landfill. This implies a total evaporation concept without any liquid purge from the plant. A purge typically allows the control of build-up of impurities in the plant. This usually results in specific physical and chemical properties within the concentrate such as high boiling point elevation (BPE), high viscosity, foaming, poor crystal growth and increased corrosion. In the case of inorganic effluents, the final product is usually a mixed salt and of no commercial value unless SSC may be employed – See below. In the case of organic effluents, the concentrate could be a liquid or 'sludge' and be viscous in nature. Further drying for example spray drying may be required. The key objective however is to select the optimal process, balancing capital expenditure with minimisation of operating costs.
The final product from an effluent plant is frequently of low or no value, so that capital and operating costs are usually severely restrained. PPTech have several reference plants where value added by-products are recovered through selective salt crystallisation (SSC). Some examples of this are:
Stainless steel plant
- Calcium Nitrate Concentrate which is recovered from a pickling effluent for sale into the fertiliser industry
| Petrochemical plant |
- Sodium sulphate is recovered from a mixed mine water effluent for sale to the chemical industry |
| Platinum producer |
- Sodium Chloride recovered from a mixed effluent |
| Petrochemical plant |
- Sodium Nitrate from an effluent acid stream |
| Platinum producer |
- Sodium sulphate from treated Base Metal Refinery effluent for sale into the chemical industry. |
| Vanadium producer |
- Sodium sulphate from mixed sodium / ammonium sulphate effluent on a vanadium plant. The sodium sulphate is re-used within the refining process |
PPTech have the laboratory and pilot testwork facilities which combined with our extensive experience will allow us to evaluate your specific effluent and to propose various flowsheet options. The separation of value adding by-products is investigated and based on our experience with industry in general, are able to confidently propose solutions capable of meeting your needs.
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