T1.Below is an extract from the q&a forum on how Calcium...

T1.
Below is an extract from the q&a forum on how Calcium Sulphide may be used to remediate waste. The technology is not new if one checks out the web. What is new is that INL have a facility that is physically there with the ability to treat the toxic Hunter river sludge, it does not have to be constructed.


Our development work for the Intec Metals Recycling Project showed that a little-known chemical, calcium sulphide (CaS), is very applicable to wastewater treatment, whether directly linked to the Intec Process or not. This is not completely novel, nor is it patentable IP, but it is very useful to the Project in terms of the number of business opportunities it opens up.

CaS is a superior alternative reagent for many wastewater applications because:
(1) it precipitates heavy metals at near-neutral pH (as opposed to pH 11-12 typical for most caustic soda applications), reducing the cost of reagents and the final pH of the treated water stream. Additionally, the precipitated sulphide solids floc, settle and filter well, as compared to the notoriously-difficult amorphous oxide/hydroxide sludges that result from alkaline treatment.
(2) the chemistry of heavy metal precipitation using alkali is complex, but is such that the conditions required for precipitation of many metals vary, meaning that some metals can actually start redissolving into solution as the pH is raised. By comparison, sulphide precipitation yields a pretty uniform response across most metals.
(3) the use of sodium sulphide, the better-known competing reagent, results in a build-up of sodium salts in the treated water, potentially beyond acceptable levels for the receiving system. By comparison, both the calcium and the sulphide in CaS regent precipitate, leaving a clean treated water stream; and
(4) the resulting heavy-metal sludges are highly suited to recycling via the Intec Process. As such, instead of the usual method of costly stabilisation followed by disposal to landfill, the metals can be brought back into the useful product stream.

Calcium sulphide water treatment is equally applicable to mine tailings water (which, in some cases known to Intec, can contain up to a tonne of heavy metals in every day's overflows) or industrial wastewaters. Intec has this week commenced commercial trials at the Burnie Demonstration Plant of CaS treatment of wastewaters coming from a Tasmanian industrial facility.

Although the know-how is not unique, Intec is itself fairly uniquely position with respect to sales of calcium sulphide for water treatment in that small operators can buy the CaS, precipitate the heavy metals at their own site, and then pay Intec to take the heavy metal sludges and recycle them at the Intec Metals Recycling Project. This is where our ongoing agreement with Veolia Environmental Services is important, where Veolia has the extensive network of contacts, know-how, infrastructure and transport to assist these operators (small, medium and large), collect and collate the waste, and deliver it to the Intec Metals Recycling Project in ready-to-process form.

Waste producers will ultimately save money in reagents and stabilisation/disposal costs, their wastewaters will be cleaner, and the Intec Process will offer them a superior environmental outcome for the metals contained in their wastes.

It might also be worth making the point that the word waste has very negative connotations. We need a new set of terminology. At the moment, if a water stream contains appreciable levels of copper, lead, and/or zinc, then it is classed as a waste. Precipitate those heavy metals from solution into a concentrated sludge and it is now probably classed as a hazardous waste. However, if the Intec Process is available to recycle those materials, suddenly your terminology changes: the heavy metal sludge is a valuable feedstock, and the resulting copper, lead and zinc are recycled as clean metals, saving the environment from avoidable landfill disposal and (to a small extent) saving the world from having to use copious energy to produce new metal by mining and smelting.