Borax mining and refining operations have long been extremely thrifty by industrial standards when it comes to the use of water. The U.S. Borax mine in Boron, California requires less than 600 gallons of water to produce one tonne of refined borax. Compare this to the 100,000 gallons required to produce a tonne of paper or the astronomical 350,000 gallons needed for each tonne of aluminum.
Although it’s located in the middle of the Mojave Desert, Boron has had access to water at reasonable cost for most of its history. For more than a century, local water was available from shallow, semi-potable wells, and the plant is a major customer of a water pipeline system originating in central California some 400 miles to the north. Boron's use of this imported water is key to keeping this system economically viable for the smaller residential and agricultural water users in the High Desert area.
A critical component of the water issue at Boron is its disposal once it has been used. This disposal depends simply on letting the desert sun evaporate it. Even at the prodigious Mojave Desert evaporation rate of 96 inches of water per year, it takes an enormous amount of surface area to evaporate the 700 gallons per minute of waste water discharged from the plant. This is where Boron's permitted surface impoundments, or ponds, come into the picture. Ponds supply both the required surface area for evaporation and what is known as surge capacity—enough depth to cope with seasonal variations in the evaporation rate.
Boron's Challenge: Dramatically Reduce Water Use
In the late 1990s, Boron's evaporation requirements were met by two 120-acre tailings ponds and six 20-acre reclamation ponds, all with single clay liners. However, Boron's single-lined ponds had become obsolete, and U.S. Borax committed to a long-range phase-out program, including the relinquishment of one tailings pond by the end of 1995. Mine management had to answer a critical question: Do we build a replacement or come up with some other solution?
A new 120-acre pond could have cost up to $24 million and would have taken some 18 months to construct. Obviously, such a huge expenditure just to stay in business would not be an attractive proposition for the company, its customers, or the environmental regulators. In addition to the cost issue, there would have been other serious problems: where to build the pond, what to do with the displaced wildlife, how to construct an absolutely leak-proof pond.
Instead, we opted to look for a breakthrough.
A Water Conservation Breakthrough
The complex problem-solving technique called Breakthrough Strategy had already been used successfully at Borax in connection with fines reduction and product contamination. In June 1993, a multidisciplinary Breakthrough Strategy team was assembled at Boron with representatives from production, maintenance, engineering, and power generation. This team, supported in its efforts by Robert H. Schaffer & Associates, authors of the Breakthrough Strategy approach, clearly defined the goals of a water and effluent reduction program.
After some earlier water conservation successes, it was known that a reduction of an additional 200 gallons per minute (or 8,650,000 gallons per month) in water consumption should be sufficient to make a replacement tailings pond unnecessary. Although seemingly a modest quantity, 40 years of previous effort at water reduction said that this was an unachievable goal without some major innovation.
The Breakthrough team found the needed innovation. It determined that if water could be used more than once—recycled—a real reduction could be made. In order to achieve this, however, a very large holding tank was required as well as a system of pipes and sumps to collect and return used water to the holding tank and to supply the various plant users from the tank.
The obvious choice for the holding tank was one of the primary process thickeners. A thickener would be ideal because of its immense size—3,500,000 gallons—and its ability to remove solids from recycled water.
Within a month, plant maintenance had converted the No. 4 thickener to a recycled water clarifier and holding tank, and tied together the necessary collection and distribution system. Almost from the day that this was accomplished, water use dropped and discharge to the tailings ponds declined—dramatically.
Dramatic and Sustainable Environmental Conservation Improvements
Boron's water and effluent reductions were real and sustainable. Compared to historical levels, typical monthly water usage dropped from 58 million gallons to 47 million gallons by early 1994. With less water being used, the plant's effluent discharge to the existing ponds was reduced 27% from 41 to 30 million gallons per month. This meant the existing ponds were quite able to handle the plant's discharge requirements.
After 15 months, the full impact of the Breakthrough Strategy could be summarized and quantified. An old tailings pond was taken out of service two years ahead of schedule. A water consumption reduction of 250 gallons per minute was accomplished, beating the target of 200 gallons per minute. Most important, the remaining ponds could handle the plant's liquid discharge requirements.
Since then, U.S. Borax has continued to search out ways of reducing overall water use as well as the volume of liquid discharges to ponds, with the goal of further reducing the need for ponds.