Silver nanoparticles could aid clean-up of mercury in water

A process for creating extremely small silver nanoparticles could usher in more effective, cheaper ways of cleaning mercury-contaminated water.

The team at Brighton University says the particles themselves could then be incorporated into industrial processes that use mercury or small-scale filters for dentists and jewellery manufactures.

Amalgams, which are alloys of mercury and other metals, have been used for more than 2,500 years in the production of jewellery and dental fillings, and for the extraction of metals such as silver and gold in mining operations.

However, when mercury is released in industrial waste and gets into water supplies it has a major environmental impact, as project lead Dr Kseniia Katok of Brighton explained to The Engineer.

In the 1990s, Squamish in Canada was subject to a huge clean-up following mercury pollution from its forestry industry — with the cost of the cleaning chemicals alone running into tens of millions of dollars.

Brighton’s cost-effective alternative first involves mixing silver with specially modified quartz sand, which reduces silver particles to a nanoscale with a high degree of purity.

‘Other methods such as citrate reduction may leave residual organics in there, but in our case they [silver particles] are pure, they’re small and we can control their size,’ Dr Katok said.

This is important because when the diameter of the silver nanoparticles drops below a critical 32nm they attain a property called ‘hyperstoichiometry’. The upshot is that the ratio of mercury to silver goes from 1:2 to around 1.5:1 — effectively cleaning up contaminated water with less silver.

‘You could put it in some kind of filter and pour through contaminated water, so the mercury will be immobilised on the surface of the silver nanoparticles, so you will have pure water coming out — for example, in a dentists when they remove fillings from teeth they could use this,’ Dr Katok said.

The group will also look at ways of scaling up both the production of the nanoparticles themselves and their deployment in various scenarios.

Project collaborator Andy Cundy, professor of applied geochemistry at Brighton, said: ‘These findings enable a major shift towards the use of nanomaterials for waste-water remediation and metal removal and recycling. We envisage that this composite can cheaply and effectively be incorporated into a variety of configurations.’