Chemical & Engineering
NEWS AUGUST 10, 1970
Reduction cells at world's largest aluminum plant, Alcan's at Arvida, Que.
NEW TECHNIQUE FOR ELECTROCHEMISTRY
PPG caustic-chlorine plant Reactions with limitations
Electrochemistry has been something like electricity with motors but no generators. Almost by definition, it has been concerned with the phenomena that occur in an electrolyte under the influence of an electrical current. But why not move the electrolyte through a magnetic field and create the same phenomena without the need to apply an external electrical current—and at the same time bypass some of the limitations of conventional electrolytic reactions? That's how Richard L. Davies reasoned, and he now has a newly issued patent (U.S. 3,522,162) on process and equipment that could well form the basis for an entirely new field of electrochemistry. Mr. Davies is president of Klein & Saks, Inc., a Washington, D.C., management and technical consulting firm which has for years served not only companies but industry groups such as the Synthetic Organic Chemical Manufacturers Association and the Pharmaceutical Manufacturers Association. He was a cofounder in 1940 of the Chemical Market Research Association. Conventional electrolytic reactions involve a stationary electrolyte in which electrodes are immersed. The basic phenomenon is the migration of ions or electrically charged particles in the electrolyte under the influence of an electrical current applied to the electrodes.
Over the years, this phenomenon has become the basis of a vast industry. Chlorine and caustic soda are produced in electrolysis cells. So is aluminum. Electrolytic techniques are one way of producing oxygen, hydrogen, fluorine—and copper. Electroplating makes use of the phenomenon, as do more recent processes for oxidation and reduction reactions of organic chemicals. The new development doesn't make all of this obsolete. Despite the success of electrolytic processes, certain limitations are inherent in the technique. Not the least is that electrolysis products build up around electrodes, shielding them and limiting reactions to the electrode/electrolyte interface. Mr. Davies explains that with the new technique, energy can now be applied directly to ions or particles anywhere in the electrolyte. Energy can be applied strongly in one part and weakly in another. Or it can be spread evenly throughout. The technique can be applied to various types of processes: electrolysis, oxidationreduction, electrophoresis, and electrodialysis. The new technique makes use of a magnetic field—generally radial. Containers of electrolyte are moved perpendicularly with respect to the field, generating a potential difference across the electrolyte. Electrodes at each end AUG. 10, 1970 C&EN 13
of the container are connected in a closed circuit. Numerous variations can be worked on this theme. With a centrifuge arrangement electrolyte can be whirled through a field formed by having one magnet pole in the center and the other around the periphery. Or electrolyte can be pumped through a helical coil wound around a stationary drum. Or the field can be moved through stationary electrolyte. In one specific experiment recorded in the patent, Mr. Davies used a 3 3 / 4 -inch-long, 1 / 4 -inch-diameter plastic tube as the electrolyte container. It was held on the periphery of a 51/:2-inch-diameter drum revolving at 2700 r.p.m. With an electrolyte of saturated stannous chloride solution with a suspension of the same, one of the tube's copper end plugs became coated with metallic tin. Mr. Davies is prepared to provide assistance or custom-built apparatus to companies wanting to experiment with application of the new method to their specific problems. He also plans to provide demonstration equipment.
sulfide to a sulfate or chloride; recovery of elemental copper; and regeneration of the leaching solution, which may include recovery of byproducts. (Recycling minimizes water pollution.) Duval's process and a process under development by Dr. Richard Snow at IIT Research Institute involve solutions of metallic chlorides such as ferric chloride to convert copper sulfide to the chloride. Subsequent recoveiy of elemental copper can be done by various methods such as "cementing" (precipitating) with sponge iron, electrowinning, precipitating cuprous chloride and reduction with hydrogen, or other methods. Regeneration of the leaching solution can be done by air oxidation. Other processes, such as those being developed by Anaconda Co.—technology of Treadwell Corp.—and Sheritt Gordon Mines of Canada, require use of concentrated sulfuric acid or dilute sulfuric acid and oxygen to convert the copper to the sulfate. Elemental copper is recovered by precipitation as a cyanide and reduction with hydrogen, or electrolysis. In other chemical processes copper oxide can be leached with dilute sulfuric acid as is done at Bagdad Copper, Bagdad, Ariz. The sulfate is reduced in batch reactors with hydrogen to give copper powder, which is dried and sintered to remove trace impurities such as oxygen and sulfur. Cost estimates of wide use of hydrometallurgical processes are complex. Direct comparison of the costs of hydrochloric and sulfuric acids is impractical in assessing processes that use metallic chlorides because costs of other pollution abatement efforts are so significant. Incremental values of higher recovery of copper and of byproducts are cost considerations.
COPPER:
MERCURY:
Clean Smelting
Other Metals Suspect
Government and public outcry over air pollution from smelting copper ores may force changes in the copperproducing industry faster than any new development since the Bronze Age. The pressure has caused every major U.S. copper producer to explore hydrometallurgical processes and has led some to invest heavily in development of these processes. Most of the processes are still in developmental stages, but among those in pilot-plant stages, the process of Duval Corp., a subsidiary of Pennzoil United, Inc., Houston, Tex., is claimed to be pollution-free. The hydrometallurgical processes used on copper sulfide ore concentrates have three parts: conversion of the
The recently concluded Senate mercury pollution hearings have raised a nagging question: Will pollution from heavy-metal sources be "discovered" as the next environmental crisis? Thus far, not much of a case for a "crisis" exists, but the metals will receive much more attention soon. Philip A. Hart, chairman of the Senate Subcommittee on Energy, Natural Resources, and the Environment, will reopen hearings on mercury and "other heavy metals," probably late this month. The Michigan Democrat is looking for an early warning system that would be capable of preventing future "mercuries." He is urging passage of the Magnuson-Hart Commer-
Inventor Da vies Basis for new field
14 C&EN AUG. 10, 1970
THE CHEMICAL WORLD THIS WEEK cial Technology Assessment Act and of its proposed environmental data bank. He will also amend a pending public works spending bill to step up funding to inventory U.S. waters for elements discharged into them under a recently revived antipollution law, the 1899 Refuse Act. Under questioning by Sen. Hart, Carl Klein, Interior Assistant Secretary, admitted that "substantial quantities" of arsenic and lead are being discharged into Louisiana waters from unnamed industrial sources. However, the intrastate nature of the situation prevents federal action from being taken. Also disclosed was that a rough target for now for mercury discharges is 0.5 pound per day, although alleged mercury polluters will be handled on a case-by-case basis. Interior has had mercury and other heavy metals under study for months. Without ranking the metals as to the water pollution hazard they represent until more hard data come in, Interior's Victor Lambou says the list includes chromium, cadmium, zinc, copper, cobalt, arsenic, barium, tin, manganese, nickel, and lead. The Texas Water Quality Board will hold hearings on proposed regulations for these metals (except for cobalt) and mercury next week. Late this month a study by the Federal Bureau of Water Hygiene is due on water supplies for 989 communities. The study finds excess lead, copper, and zinc in some water supplies, from natural as well as industrial sources, says a BWH official. Meanwhile, the National Academy of Sciences has started to assemble experts to study heavy-metal pollution.
Michigan's Hart Preventing future "mercuries"
