Chrome Precipitation

Casino Hide Tanners - NSW, Australia

Michael Walsh \ July 9, 2019
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Home \ Water & Wastewater \ Chrome Precipitation at a tannery, Casino Hide Tanners
ACTI-Mag is a highly reactive, concentrated and stabilised suspension of Magnesium Hydroxide manufactured by hydrating ultra high surface area Magnesium Oxide at Casino Hide Tanners, NSW, Australia.

case study summary

Challenges
  • Magnesium Oxide (MgO) is difficult to hydrate
  • The hydration process is very labourious
  • large quantities of MgO remains un-hydrated, thus being unavailable for chromium precipitation
Objective
  • Reduce cost by eliminating MgO hydration from waste water processing.
  • Efficiently precipitate chromium in waste water system
Solution

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ACTI-Mag is a highly reactive, concentrated and stabilised suspension of Magnesium Hydroxide manufactured by hydrating ultra high surface area Magnesium Oxide at Casino Hide Tanners, NSW, Australia.

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Benefits of ACTI-Mag

Calix ACTI-Mag is already pre-hydrated and ready to use.

The resultant slurry also has a high pH and a high surface area.

Therefore, it is more effective in Chromium precipitation.

Introduction

Established in 1975, Casino Hide Tanners (CHT) – a part of the Northern Co-op Meat Company (NCMC) – was one of the first tanneries in Australia dedicated to the tanning of cattle hides for export. Over the years, additions to the tannery have made it one of the larger installations in Australia, currently processing about 600,000 cattle hide per year.

Located on the same site as the abattoir, the hide is received immediately after slaughter and put directly into production. On arrival, the hide is then fleshed at the tannery, with weight being carefully recorded prior to and after fleshing. By using 24 tanning drums, the hide is then loaded for de-hairing and eventually tanning.

Challenges

In the industry, Chromium (III) Oxide is used as a tanning agent to produce ‘Wetblue’ as a precursor to finished leather. Waste liquors from the Sammying stage of production still contain levels of chrome, which must be removed from the wastewater prior to discharge.

Conventionally, Chrome is precipitated by raising the wastewater pH to approximately 8.5, which minimizes the solubility of Cr2O3 and precipitates it as a sludge that can be removed by filtration.

In early 2016, Casino Hide Tanners built a new Chrome Precipitation plant to replace the previous plant. Prior to that, they used Magnesium Oxide (MgO) which was hydrated with water to produce Magnesium Hydroxide – Mg(OH)2, which was used to precipitate the Chromium prior to dewatering on a band press filter.

However, MgO is notoriously difficult to hydrate and the process was labor intensive.

Casino Hide Tanners also observed that a lot of MgO remained un-hydrated and was therefore not available for precipitation of Chromium.

 

The highly porous Calix MgO particles result in ACTI-Mag particles that have high surface area, pH & reactivity to more effectively nucleate Chromium precipitation and achieve improved performance.

As such ACTI-Mag is applicable to precipitation of a range of metals in waste stream not just chromium.

Solution

In January 2016, Casino Hide Tanners installed and commissioned a new Chrome Precipitation plant. This comprised a reaction tank, followed by a dissolved air flotation (DAF) for water clarification, prior to dewatering of DAF sludge through a plate filter press.

After discussions with Calix, Casino Hide Tanners made a late design change to replace the planned new MgO hydration plant with a bulk storage tank to enable use of ACTI-Mag, highly reactive Magnesium Hydroxide.

 

ACTI-Mag is a concentrated, stabilized suspension of Magnesium Hydroxide, an inorganic compound with the chemical formula Mg(OH)2.

ACTI-Mag, produced by Calix’ patented Calix Flash Calcination (CFC), is highly reactive due to the very high surface area of MgO. The highly porous MgO particles produced by CFC hydrates far more readily and results in highly reactive Mg(OH)2 product with a high surface area.

Conclusion

The use of Magnesium Oxide basifying agents in the leather tanning process is a worldwide industry practice.
Magnesium Oxide is a simple chemical, but a complex material. Different types of processing, sources of production, and end-use requirements result in products with very different physical characteristics, although chemically very similar.

Casino Hide Tanners originally planned on hydration by using MgO powder, as it is traditionally done in this industry and many others. But the understanding of ACTI-Mag’s ease of use and reactivity due to its high surface area led them to become one of Calix’s happy customers.
ACTI-Mag is very effective at precipitating metals due to its high surface area & particle pH ~ 10.4 and may therefore allow better performance at a lower bulk solution pH.

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Boosting anaerobic digestion, ACTI-Mag supports bacteria and speeds up the breakdown of complex organic chains (including proteins, carbohydrates and lipids) into smaller units such as amino acids, sugars and long chain fatty acids. The process reduces the rate-limiting step in the digestion process. This results in improving BOD/COD in the final effluent.

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