Absorbent clay key to clean farms

Zeolite has been used in the pitch at Westpac Stadium. Photo / Mark Mitchell

Super-absorbent mineral has the potential to stop agricultural pollutants from entering streams and lakes.

A mining sector group says New Zealand should be doing more to capitalise on the "alchemist's dream" of using pollution-soaking clay to clean up dairy land.

The NZ Minerals Industry Association says zeolite - which has an open crystal structure and is super-absorbent - could be used to soak up the nitrogen and phosphate from dairy farms that is polluting streams and lakes.

The mineral is used to soak up oil spills, in kitty litter, to absorb barbecue fat and in sports stadium turf at Westpac Stadium in Wellington and Waikato Stadium.

Association chief executive Doug Gordon said encouraging development of "green minerals" had the potential to change public perception of the sector. Capturing farm run-off in zeolite-laced pastures would save waterways and fuel grass growth.

"You've got your alchemist's dream, turning muck into gold."

Scientists at Crown Research Institute Scion modified the mineral to act as a binding agent that attracts phosphorus and other polluting nutrients that run into waterways.

Removing excess phosphorus and other nutrients from the water reduces unwanted algal blooms.

Related mineral bentonite could also take pollutants out of waste from paper mills and freezing works.

"These minerals have been little explored or developed in New Zealand due to the lack of investment both from a government and market perspective," he said.

The indirect benefits from local and foreign investment in "green minerals" ranged from increased tourism to the rehabilitation of water quality and habitats of endangered species.

"To not explore this further is foolish," said Gordon.

Commercial applications of modified zeolite are promising. Potential uses include treatment of lakes, irrigation reservoirs, domestic and commercial fish ponds and aquariums, farm dams and troughs, golf course ponds, water storage systems in nurseries and other irrigators.

Rotorua-based Scion started research on zeolite in 2004 and two years later teamed up with Tokoroa's Blue Pacific Minerals to develop technology based on the absorbent properties of the mineral.

Trials have been conducted at Lake Okaro, a small nutrient-rich lake south of Rotorua, from 2006 and a trial programme has been used at Lake Rotoiti.

Managing director of Blue Pacific, Dave Hill, said the firm had consent to extract about 100,000 tonnes a year but mined about half of that. The firm has 24 fulltime workers and has grown strongly in the past 10 years.

Most zeolite was used as a fat absorber for barbecues, oil absorbent for spills, fine powder that can absorb toxins in stock food, and used in sports turf, including golf courses.

He said a barrier to wide use on dairy farms was the need to drill it into pastures or pack it into trenches, which is expensive.

"It's a matter of having a pragmatic commercial reason. You can load up zeolite with nitrogen fertilisers that helps pay to get the product into the ground."

Super soakers

*There are about 40 minerals known as zeolites.

*They are commonly found in volcanic rocks.

*Zeolites have a unique open crystal structure with many surfaces.

*This provides a huge surface area for chemical exchange and absorption.

*Animal wastes could be tied up in this layer and waterways protected.