Metals often need to be recovered or removed from aqueous process streams, effluents or drainage in the Mining and metallurgical industry. In order to economically recover these, or to comply with environmental regulations, metals are often removed by means of chemical precipitation, like a neutralisation/precipitation to form hydroxides. This results in bulky, often impure sludges that can be difficult to further process or sell. In addition, the large volumed result in high costs when the sludge cannot be reused and needs to be disposed off.



An alternative is a precipitation in the form of sulphides. The application of H2S generally leads to better metals removal efficiencies and a product that is more compact, stable and re-usable than metal hydroxides or carbonates, The quality is generally also higher, allowing better reuse. Often, the value of the metal product can balance the costs.

However, a common problem is to have an economic, safe and reliable source of sulphide because typical sources (like sodium sulphide, NaSH, or liquid H2S) have disadvantages.

PAQUES has developed a cost effective and efficient alternative to the traditional sources of sulphide: THIOTEQ™ Biogenic H2S Production. In this innovative process H2S is produced on-site from a sulphur source (elemental sulphur, sulphuric acid or another sulphur source) and an energy souce (electron donor) such as ethanol, acetic acid, hydrogen gas etc. Feedstocks are seleceted based on local availability and size of the installation.

Advantages of THIOTEQ™  technology (compared to NaSH or ‘chemical H2S’)
· lower costs per tonne of sulphide produced;
· safe process at ambient conditions;
· no transport and storage of hazardous sulphide is required;
· better selectivity for metals; higher product quality;
· flexible process, production on demand;
· robust and proven process.

Technology
The system essentially comprises of a reactor where the H2S is generated and a gas/liquid contactor.

The sulphide is transported by menas of a gas recycle to the contractor where the waste stream is contacted with the H2S and the formed metal sulphides are separated from the liquid stream. This controlled precipitation process results in better settleable particles than what is normally obtained with a sulphide precipitation process.

This process is typically suited for a sulphide demand of 100 kg to 10 ton/day. Economically attractive metal concentrations range from a dozen mg/l to several gram per liter. For lower concentrations we recommend BIOMETEQ™ technology. Please have a look at SULFATEQ™ technology when you want to remove sulphate and metals.