Refiners developing ways to deal with waste

At Valleyfield near Montreal, a technical committee set up by Electrolytic Zinc of Canada has met to decide which of the competing technologies developed since the early 70s have the most promise for dealing with the company’s iron sulphate waste and should therefore receive the support of this Noranda Group company.

Electrolytic Zinc is fortunate that its tailings pond is located on a thick layer of impermeable clay. But to build another pond to accommodate future zinc production would cost the company three times what it did to build the original facility.

Other non-ferrous refineries in Timmins, Sudbury, Fort Saskatchewan, Bathurst and Baie Comeau, to name a few, are less concerned about space for new residue ponds but are equally concerned about the acidity of their effluent and its metals content. It is estimated that mining companies spend $100 for every tonne of waste iron they must contend with.

The environmental devastation that occurred in Timmins, Cobalt, Sudbury and other Canadian mining towns at the turn of the century due to shoddy waste treatment practices can never happen again, says V. I. Lakshmanan of the Ontario Research Foundation. Government guidelines regulating the acidity of emissions and the concentration of metals such as arsenic, lead and cadmium from tailings and residue ponds have become very strict.

“We are putting out 1% of what we used to put out legally five years ago,” says David D. Rodier, mill manager at Electrolytic Zinc in Valleyfield, Que. Hydrometallurgy

Aluminum, uranium, copper, zinc, and nickel refiners worldwide are coming to grips with the demands placed on them by society by developing new technologies that deal with the iron that occurs in most mine concentrates. Reflecting the concern of metallurgists worldwide, some 200 attended an International Symposium on Iron Control in Hydrometallurgy in Toronto this week, organized by the Hydrometallurgy Section of the Metallurgical Society of cim. In the audience were representatives from 21 countries, according to John E. Dutrizac, head of the Metallurgical Chemistry Section of canmet and conference chairman.

By producing some 25.8 million tonnes of copper, zinc, lead, nickel and aluminum in 1983 the non- communist world produced an estimated 19.3 million tonnes of iron waste, according to the snc Group, a major engineering company in Montreal. Added to that is several millions of tonnes of iron dust produced in the electric furnaces of the world’s steel makers and the iron-rich wastes produced by the pickling process used to galvanize and plate steel. In the case of zinc most concentrates treated by smelters contain 8%-10% iron and 50%-52% zinc.

By efficiently handling the iron, metallurgists have found that most of their problems concerning heavy metals is taken care of at the same time — the iron acting as a carrier for the other metals. National quidelines call for a minimum of 5 mg of iron per litre of water. “If the iron were not there it would be more difficult to deal with the problem of heavy metals,” says Dr Andrew J. Oliver, head of hydrometallurgical research and development for Eldorado Resources.

Traditionally iron has been stockpiled by refiners in huge residue ponds. But now with regulations making it more and more difficult to obtain permits to construct new ponds in heavily populated areas, refiners are looking for technologies that will produce an iron product that can be sold or given away to steel manufacturers. With high- grade iron deposits being developed at grades of 70% in Brazil the challenge is a tough one. Refiners estimate they can compete successfully by producing a product that grades 60% iron. Competing Technology

The competing technologies to deal with iron include:

*Jarasite Precipitation — Originally developed in the early 1970’s in Australia, researchers are now attempting to produce a cleaner hydrous sulphate. This technology is used in 18 plants worldwide.

*Goethite Precipitation — This method was developed in 1975 and is used in five plants. Researchers are now attempting to make the technology more acceptable.

*The Ruhr-Zink Hematite Process — was developed just recently in 1978 and is used in two plants, one in Japan and one in West Germany. Although it is currently a very high cost method it is considered to be at the leading edge of what is coming to North America.

*Solvent Extraction — This technology has been well established in the copper and uranium industries for years but has recently attracted attention in the zinc industry for its potential to produce various salts which have potential for marketing.

*Pickle Liquors — This method has been well established for galvanizing and plating steel but is now being extended into the production of stainless steel. There could be potential for selling pigments produced from the process as a way of generating additional revenues.

Two emerging technologies include:

*The RPC Sulphation Roast-Leach Process — which has been studied for 10 years in the laboratory and pilot plant stage in Bathurst, N.B.

*Chloride Leaching — which may find a niche where the feedstock is more complex chemically.

It has even been suggested that the ferrite powder produced when versatic acid is used to seperate copper from iron by solvent extraction could be marketed as a raw material for making high-tech ceramics.