The resulting copper sulfate powder can be used in fertilisers, and ChemRecovery has supplied 150 tonnes of the extract to a New Zealand fertiliser company.
The company is also an exporter. It has sold more than 50 tonnes of another metallic compound, vanadium oxide, to a Chinese customer.
Processes have also been developed in the lab for recovery of cobalt, nickel and zinc, and the company is working on commercialisation.
It has already reached that stage with another copper product, copper powder, which the company says has been shown by University of Auckland and University of Waikato analysts to be of world-market standard. It is attracting interest from buyers in the US, China and other countries.
Compared with the copper wire for which thieves risk life and limb, copper powder is 100 times as valuable.
ChemRecovery owner Jafar Davari says the powder is worth US$800,000 a tonne and the company can produce about 18 tonnes a year. Demand from the electronics industry, which uses it to make a conductive paste, explains its high price.
ChemRecovery grew out of an earlier business, ChemWaste, which processed industrial waste for dumping, with no attempt at metal extraction.
But it was decided to change course, leading to the sale of ChemWaste and development of chemical processes to recover valuable metals.
It has taken three years to work out how to extract the copper powder from liquid waste. As sales begin, Davari expects the company to double in size to more than a dozen staff.
The business fulfils New River's environment-improving criterion on two fronts: by reducing the quantity of toxic waste that must be disposed of and recovering rare elements. It's an activity Iran-born Davari, a chemical engineer, is glad to be in.
"It's the whole philosophy of the business," he says.
#2. Stonewood Homes: building greener houses
Stonewood Homes is the solitary building company on the Green 50 list, vindicating a decision eight years ago to set itself apart by emphasising sustainability.
"Building green homes is our underlying ethic," says Brent Mettrick, Stonewood's founder and managing director.
The company started out in Christchurch in 1987 and via franchisees it now builds homes from the top to the bottom of the country, erecting more than 400 last year.
It will build more than that in Canterbury alone this year, as the post-quake rebuild gets into gear.
Mettrick says he had a green building awakening at a conference in the US in 1995, and returned to New Zealand ready to paint Stonewood that colour. "But I looked around and thought, no, the market won't take it."
It was 2004 before Mettrick made his move. "That's when we came out with a green format, green thinking and started to embed it in our business."
Stonewood's homes are highly insulated, feature appliances that minimise power and water use, and are built using renewable resources and non-toxic materials.
Its flagship design is a seven-star rated home with energy-efficient heating, water heating and lighting, and extra insulation.
The star rating system ranks homes on a scale of one to 10, with homes built to the current building code getting four stars.
Of the 400 or so homes it will build in Christchurch this year, about 70 per cent will be rated at five stars or above, Mettrick expects.
He acknowledges that Stonewood's homes are a shade of green that may not satisfy the most ardent environmentalist - the company sometimes gets called a "greenwasher" - but says they match what the market is prepared to pay for.
"Ultimately we have to be a successful business. Green building will not succeed if it has to be propped up through subsidies, yet while most buyers of new homes like green features, they don't want to pay more for them."
That means persuading them to see beyond the upfront cost comparison between an environmentally friendly home and a dwelling that is not so green.
"It's actually about the liveability, the enjoyment and the return you get on your home long term. For us as a business it does differentiate us from our competitors, which are generally conservative in the green area.
"We just get on and build green houses."
#3 Reid Technology: power from the sun
Reid Technology's third placing on the Green 50 list was earned by its solar energy business. The irony, says managing director David Reid, is that environmental considerations are not the main focus for most of the company's customers.
"The [low] environmental impact is a significant benefit but it is not the main driver," he says.
A typical example is a $7.9 million NZ Aid Programme-funded project the company is working on in Tonga with Meridian Energy.
The 1MW Popua solar power plant will supply the main island of Tongatapu with about 4 per cent of its electricity needs, cutting diesel generator fuel consumption by nearly 0.5 million litres a year.
"They'll be less dependent on imported diesel, which is only going to get more expensive, so they will save money in the longer run. And at the same time they'll be cutting down on diesel exhaust pollution."
The project will begin producing power in August.
For remote locations, where a unit of power costs 70 to 90 cents, a tipping point has been reached, and solar - or photovoltaic - generation is competitive with diesel generators.
Reid Technology, a third-generation family firm, has made a specialty out of installing solar systems offshore, with locations including Great Barrier and Raoul islands.
The uptake of solar power in this part of the world has benefited from northern hemisphere governments' support for the technology, Reid says, particularly in Germany, Spain, Italy and California. That has led to an expansion of manufacturing output.
A further spur has come from an unlikely quarter. "As governments have looked to make cuts because of the global financial crisis - Australia has had solar incentives turned off and on a bit like a tap - solar manufacturers have been left with excess capacity. So, as they look for new markets, the price of solar modules has fallen rapidly over the past two to three years."
The point isn't far off where it will be viable to make solar generation a feature of any New Zealand home, Reid reckons.
"We have no incentives at all in New Zealand, which makes it hard, but it means when it gets going I think it will work in the longer run."
Small-scale solar also has the benefit of not being a blot on the landscape so it avoids the fights that surround bigger projects.
"I say to my team all the time that if we do our job well it's good on many levels. It's good for clients in that they get power in difficult places that is cheaper in the long run, it's good for us because we get to do interesting work in interesting places, and it's good for the environment."
