Introduction

Mary Ruth Corporation was formed in 1955 by Milford Jenkins. Mary Ruth has operated surface and deep mine operations in northern West Virginia and Maryland for the past 38 years. In 1972, Mike Jenkins began working with his father in the business. During the 1970's, Mary Ruth operated as many as seven active mines and a coal preparation plant employing nearly 100 people.

Acid Mine Drainage

Several of Mary Ruth’s surface mining operations were in the Upper Freeport seam of coal in Preston County, which often produces acid mine drainage (AMD) upon disturbance. Some of these sites required constant water treatment. In the late 1970's, caustic soda was most often used to treat water, but with time it became too costly to use.

Hydrated lime was substituted for caustic soda wherever possible. Lime was much cheaper to use, but application of the lime required a pump to circulate the pond, plus a man to feed lime slowly to the pump for mixing. These two factors made the use of lime very labor intensive and too costly. Also, about 50% of the lime that was applied did not dissolve and ended up on the bottom of the pond in spite of mixing. If the labor costs and the slow reaction problem could be reduced or eliminated, treating AMD with hydrated lime would reduce chemical treatment costs by 50 to 80%.

Aquafix Machine

As time went on, it became obvious that if hydrated lime could be introduced to the pond slowly and continuously, treatment of the water could be controlled and water quality could be enhanced. Close to 95% of Mary Ruth’s sites where AMD treatment was needed had no power to operate any kind of feeder or mixing system. So, Mike decided to use a "water wheel’ concept, which could be driven by the flowing water itself. Through the efforts of Darwin Ringer (Mary Ruth’s first employee in 1955), Robbin Ringer, and Milford and Mike Jenkins, the first water-powered lime feeder was built in 1980.

Hydrated lime was initially used in the machine, but even with several modifications over time, the hydrated lime did not feed continuously without bridging and plugging the hopper. After approximately one year of working with this original machine, Mary Ruth’s water problems lessened and so the "water wheel’ machine was placed behind the shop to collect rust.

In 1989, Mary Ruth resumed water treatment. The rusted old lime feeder was dragged out from behind the shop and a pelletized lime material was sought to use in the machine. Pelletized hydrated lime was unavailable, but a pelletized calcium oxide product was (pebble quicklime). The pebble quicklime material was loaded in the hopper of the "water wheel’ and it fed continually, solving the bridging and plugging problems in the hopper.

Quicklime is highly reactive, economical, easy to handle in 50-pound bags (or quicklime can be bought in bulk if necessary) and feeds without sticking. Water pH is rapidly raised to about 9.0, and metals in the water precipitate in settling ponds. In addition, the AMD sludge generated with quicklime is denser and precipitates quicker than caustic-generated AMD sludge.

Application of pelleted quicklime to AMD with the water wheel requires a 75- to 150-foot ditch or channel where the quicklime can disperse on the bottom of the channel. Here, the quicklime continues to dissolve over time providing a slight buffer for higher flows.

Since 1991, the Jenkins’ have been manufacturing and selling the Aquafix Machine to coal, metal, clay, and sand mining companies. In 1993, they made the first small version of the Aquafix Machine for sites that need very little treatment. It holds only 500 pounds of quicklime (while the normal-sized machine holds about 2000 pounds of quicklime) and can be moved and set up by hand with three or four people.

In 1994, the Aquafix machine fed quicklime so uniformly that silos were placed over the machine to feed into high flow AMD treatment situations. The machine can be bolted to a free standing silo of any size where a large quantity of lime is needed or where the customer would like to use bulk lime deliveries. In 1998, the silo machines were changed so they could also be used with a powder form of material such as kiln dust.

In 1994 and 1995, the U.S. Department of Energy conducted a test with an Aquafix machine at the Crystal underground copper mine at Butte, Montana. In 2000, EPA tested one of the machines at the Summitville Mine in southern Colorado.

As of 2001, 86 normal-sized, 59 small-sized, and 14 silo machines were in use. Aquafix machines can be found in western U.S. states (Colorado and Montana) southern states (Arkansas, Louisiana and Missouri), and throughout the east (Illinois, Kentucky, Maryland, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, anbd West Virginia).

The newest innovation is the use of a mixing unit, which will eliminate the need for a rock-lined ditch.

Other companies have produced a similar water-wheel system that slurries the lime before application. The results of preliminary field tests have shown a 30 to 50% reduction in lime usage and virtually no undissolved lime was entering the pond with these slurry systems.

Cost of Chemical Treatment in 1993

To estimate the potential treatment cost of using pelleted quicklime on your site, it is known that two pounds of quicklime (CaO) neutralizes the same acidity as one gallon of 20% caustic soda (NaOH), or one pound of ammonia. Based on 1993 prices, chemical costs were 6 cents per pound ($120 per ton) for quicklime, 60 cents per gallon for 20% caustic, and 25 cents per pound ($500 per ton) for ammonia.

In 1993, one operator calculated the Aquafix unit paid for itself in less than a year. Caustic soda was used previously on the site to treat an average flow of 25 gpm and 1100 mg/L of acidity at a cost of $245 per day, or about $80,000 per year. With the Aquafix System, the same water was treated at a cost of about $75 per day, or about $28,000 per year, a cost savings of about 65%. Similar cost savings were found on several sites we surveyed in 1993.

Cost of Chemical Treatment in 2001

Another way of comparing treatment costs is based on the cost to treat 1000 gallons of water. At one AMD treatment site in northern West Virginia, the cost for treating 1000 gallons of this particular AMD was $1.40 using ammonia, while the cost for quicklime was $0.53. This represents about a 62% cost savings. In addition, the treated water generated about 45% less sludge using quicklime compared to ammonia. The problem at this site with using quicklime was that the short channels did not allow suitable mixing and channel lining for optimal treatment.

At a site in southern West Virginia, 1000 gallons of AMD were treated at a cost of $0.69 using caustic soda (cost of 20% caustic was $0.43 per gallon), while this same amount of AMD was treated at a cost of $0.11 using quicklime (cost of quicklime was $100 per ton). The flow was around 250 gpm, so annual treatment costs were reduced from $87,000 using caustic to $14,000 using quicklime (84% cost reduction).

In Clay County, a 25-gpm flow of AMD was treated for $5,369 per year using 20% caustic, $2,328 using ammonia, and $1,534 using quicklime. Again, the cost savings were 71% with quicklime over caustic, and 34% with quicklime over ammonia.

Three of the four lime dosing machines used by the Maryland Bureau of Mines are Aquafix machines, and silos have been installed over the water wheel. The major advantages of using the Aquafix machines in Maryland are: 1) the ability to dose large quantities of alkaline material during high flows and small quantities during low flows, and 2) the ability to dispense various materials such as pebble quicklime or kiln dust as a powder and larger-sized, alkaline sand materials. The versatility of using different materials has been very beneficial in cost savings at these sites.

In Maryland, the Aquafix machines treat an average of 4000 gpm of water, and has returned the North Branch of the Potomac River back to a fishable waterway. The dosing has also neutralized the AMD in Jennings Randolph Lake. The original pH 5 water discharged from the spillway at the dam has been increased to pH 7 or above since the installation of the lime dosers. Cost for treating this water is about $50,000 per year, or a little more than $0.02 per 1000 gallons of water.

Conclusion

On sites where quicklime is used in place of caustic soda or ammonia for treating AMD, the cost savings have ranged between 30 to 80%. The Aquafix system may not be suitable for every site because of site constraints, water flows, or water chemistry, but in general, at most sites, the use of the Aquafix machine with quicklime has demonstrated efficient and cost effective treatment.

Acknowledgments

Thanks are expressed to Tiff Hilton, Ed Lyons, and Ted Wall for water quality and treatment cost data, as well as pictures for this article.