permaculture

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BBC News - 'Super sand' to help clean up dirty drinking water
http://www.bbc.co.uk/news/business-13895077

Contaminated water can be cleaned much more effectively using a novel,
cheap material, say researchers.

Dubbed "super sand", it could become a low-cost way to purify water in
the developing world.

The technology involves coating grains of sand in an oxide of a widely
available material called graphite - commonly used as lead in pencils.

The team describes the work in the American Chemical Society journal
Applied Materials and Interfaces.

In many countries around the world, access to clean drinking water and
sanitation facilities is still limited.

The World Health Organization states that "just 60% of the population in
Sub-Saharan African and 50% of the population in Oceania [islands in the
tropical Pacific Ocean] use improved sources of drinking-water."

The graphite-coated sand grains might be a solution - especially as
people have already used sand to purify water since ancient times.

Coating the sand

But with ordinary sand, filtering techniques can be tricky.

Given that this can be synthesized using room temperature processes and
also from cheap graphite sources, it is likely to be cost-efficient”

Mainak Majumder Monash University, Australia

Dr Wei Gao from Rice university in Texas, US, told BBC News that regular
coarse sand was a lot less effective than fine sand when water was
contaminated with pathogens, organic contaminants and heavy metal ions.

While fine sand is slightly better, water drains through it very slowly.

"Our product combines coarse sand with functional carbon material that
could offer higher retention for those pollutants, and at the same time
gives good throughput," explained Dr Gao.

She said that the technique the team has developed to make the sand
involves dispersing graphite oxide into water and mixing it with regular
sand.

"We then heat the whole mixture up to 105C for a couple of hours to
evaporate the water, and use the final product - 'coated sand' - to
purify polluted water."
Cost-efficient
Sand "Super sand" is made using regular sand - and it could become a
low-cost way to purify water

The lead scientist of the study, Professor Pulickel Ajayan, said it was
possible to modify the graphite oxide in order to make it more selective
and sensitive to certain pollutants - such as organic contaminants or
specific metals in dirty water.

Another team member, Dr Mainak Majumder from Monash University in
Melbourne, Australia, said it had another advantage - it was cheap.

"This material demonstrates comparable performance to some commercially
available activated carbon materials," he said.

"But given that this can be synthesized using room temperature processes
and also from cheap graphite sources, it is likely to be cost-efficient."

He pointed out that in Australia many mining companies extract graphite
and they produce a lot of graphite-rich waste.

"This waste can be harnessed for water purification," he said.