Aqueous process and waste streams that contain dissolved metals and sulphate are common in the metal, mining and chemical industry. The traditional method of removing both sulphate and metals is neutralisation with an alkaline agent like lime. This produces gypsum and metal hydroxides, often as a mixture. This complicates reuse of the valuable metals and results in a large quantity of sludge that needs to be disposed off.


Paques has developed the SULFATEQ™ technology as better alternative. Sulphate is converted biologically in engineered reactors into hydrophilic (non-sticky) elemental sulphur. Metals in the same (or another) process stream are recovered/removed as metal sulphides. The purity/quality of the metal sulphide product is generally so good that it is economic to sell the metal content. Dissolved calcium and magnesium are removed as carbonates. Metals and sulphate are reduced to much lower levels than lime based processes. Therefore, the effluent quality can meet stringent discharge limits.

Please refer to the THIOTEQ™ or BIOMETEQ™ technology when you are only interested in recovering/removing metals or effluent polishing.

Advantages
• Sulphate is removed effectively to <300 mg/l (200 mg/l in certain cases);
• Intermediate product (sulphide and alkalinity) is used to recover metals or to produce elemental sulphur;
• Dissolved calcium and magnesium are partly removed;
• Acidity is without consumption of neutrilsation agents like caustic;
• Applicable for fully neutralised stream (e.g. sodium sulphate solutions);
• Safe process at ambient conditions;
• Better selectivity for metals; higher product quality;
• Removes ‘difficult’ dissolved metals like manganese, selenium, thallium etc.;
• Flexible, robust and proven process (over 15 years experience with full-scale installations);
• No noticeable release of smell;
• Ecotoxicity of effluent is reduced.

Technology
Two reactors in series form the core of the process. In the first reactor a biocatalyst convert sulphate into dissolved sulphide with an energy source like (bio-)ethanol, hydrogen or an organic waste stream. The amount of sulphide is used to recover metals either upstream of the first bioreactor or elsewhere. A second biocatalyst converts the remainder into elemental sulphur in a second bioreactor using air as oxidant. The hydrophilic (non-sticky) sulphur is separated from the liquid and dewatered.

Applications
SULFATEQ™ can be used for numerous applications. The strength of SULFATEQ™ technology is that multiple problems can be solved with one installation:

• Effluent treatment in metal industry;
• Washtower acid treatment;
• Brine treatment of RO (reverse osmosis), combined with metal recovery to increase overall water recovery;
• Acid Mine Drainage (AMD) treatment combined with metal recovery;
• Effluent treatment and metal recovery in viscose industry (remove metal, sulphate and COD);
• Integration with lime neutralisation plant to improve effluent, reduce TDS and reduced sludge quantity with a better quality what results in less liability.

There are several references worldwide.