New way to deal with arsenic could pave way for B.C. mine

Metallurgical problems that have prevented the development of a gold mine near Revelstoke, B.C., may have found a solution in a recent breakthrough in hydrometallurgy.

Pilot plant tests at the U.S. Bureau of Mines Research Center in Reno, Nev., indicate a new, relatively low-cost technique known as the Cashman process should when scaled up, allow miners to safely and economically dispose of mine wastes containing the highly toxic element arsenic.

In the process, detrimental arsenic forms insoluble complexes with iron and calcium. These are left in a leach residue or sludge generated by a chemical reaction. The residue is then separated from the pregnant solution by filtration and disposed of in standard landfill sites. Precious metals are recovered from the pregnant solution using conventional techniques.

The reactions take place in a titanium reactor vessel at a temperature of 112 degrees C with steam and an air pressure of 40-50 lb per sq in. The active reagent is calcium chloride and the residence time is not more than one hour.

Artech Recovery Systems, a U.S. company listed on the nasdaq system, was set up last year to purchase a 50% interest in the process and to finance its commercialization. This week, in a private placement, that company acquired a 6% interest in tse-listed Pan American Minerals. Pan American holds a 75% interest in the J&L property — a 3.7-million-ton deposit containing gold, silver, lead and zinc, located 20 miles north of Revelstoke, B.C.

Attached to the shares are 200,000 warrants, which if exercised, will give Artech an 11.5% interest in Pan American.

Drilling and underground exploration work by BP Selco in 1983-84, indicated the deposit contains highly interesting amounts of gold (0.17 oz per ton), silver (1.72 oz per ton), lead (2.15%), and zinc (4.04%), but high levels of arsenic — as much as 4.86% by weight. That high arsenic content has until now, made development of a mine prohibitively expensive.

Arsenic must either be converted into a saleable arsenious oxide or a material that can be disposed of in an enviornmentally acceptable way. Since world markets are flooded with arsenious oxide arsenic in arsenopyrite gold ores is typically removed by roasting.

The resulting arsenic flue dust is then disposed of in a suitable area. Since arsenic is highly soluble, it can get into groundwater, rivers, streams and lakes.

In concentrations more than 0.05 mg per L (5 ppm), arsenic is highly poisonous and possibly carcinogenic in humans. Arsenic poisoning can range from chronic to severe and may be cumulative and lethal, according to the U.S. Environmental Protection Agency (epa).

Construction of a suitable disposal area is very expensive.

BP decided last year disposal would be too expensive to justify further work on the J&L property and stopped work on the ground. The company retains a 25% participating interest. Noranda Inc. looked at the property but decided not to enter into an option agreement.

After leaching a sample of arsenic sludge with humic acid for 48-hours, Artech found it could produce an arsenious sludge using the Cashman process that will meet the epa’s 5 ppm standard.

Considerable work will be necessary to develop an appropriate flowsheet and to estimate the capital costs required to treat the J&L ore using the Cashman process. Only then will a production decision be justified.

“Our experience indicates that this type of ore should respond favorably,” Sam Parks, chairman and chief executive officer of Artech says.

Pan American has 3,298,000 shares outstanding, trading at about $1.75.