its structure has been at least partially elucidated. Its catalytic behavior has also been studied earlier. But precise rate measurements have not previously been made, Mr. Cutlip points out. The Colorado workers produce the polymer by polymerizing the monomer in water at 60° C. under nitrogen, using 2,2'-azobis (2-methyl-propionitrile) as a catalyst. They then dry the polymer and press it into pellets 0.25 inch long and 0.25 inch in diameter. These are pyrolyzed, first in air and then in nitrogen, for a total of nine days at temperatures that are slowly increased from 200° to 325° C. Mr. Cutlip uses a stainless steel differential reactor to follow the alcohol dehydration, running the reaction under various partial pressures of alcohol, isobutylene, water, and nitrogen. He has made rate measurements at 240°, 260°, and 280° C. There are two proposed mechanisms for the alcohcd dehydration, Mr. Cutlip points out. One involves the transfer of electrons, the other the acidity of the polymer surface. In the electron transfer mechanism, the catalyst acts as a reservoir that either donates electrons to, or accepts electrons from, the reacting species. In the other mechanism, Br0nsted acid sites on the catalyst surface are considered as supplying protons to the adsorbed alcohol. This then reacts through a carbonium ion intermediate. The Colorado worker points out that reaction rate data alone are not enough to identify which mechanism applies. Further work is necessary. For instance, the role of electrons from the semiconductive catalyst could be examined by measuring the concentration of conduction band electrons during reaction rate and adsorption measurements. Independent adsorption studies of the reaction products, and even of the reactants, could test the validity of the proton mechanism.
Not all agree that solution mining is the only economical route, however. Shaft mining, too, has its advocates. Most notable exponent is International Minerals and Chemical's 3.5 million ton-per-day facility near Esterhazy, Sask. "In our situation," says vice president Anthony E. Cascino, "our studies show that shaft mining is the more practical route. Our operations are as efficient as we had hoped." IMC completed a 75% expansion of its potash operations last spring. Nevertheless, IMC has admitted that some of its $3 million loss for its first quarter, which ended Sept. 30, was due to the depressed worldwide price of potash. Apparently, all potash producers have been hurt by the marginal profits on potash, which now sells for about $18 a ton, down 25% in the past year. Things may get worse before they get better. IMC president Nelson C. White predicts that this year's 10% potash overcapacity will grow to about 15% overcapacity in the early 1970's. After that, he thinks, the supply-demand situation will come into a better balance. In spite of the present and future potash market problems, Mr. Jessel thinks Lynbar's new solution mining process will prove the most economical. "Compared to other solution or shaft mining operations," he says, "the new process should require far less capital cost as well as lower operation and labor costs." Lynbar has exclusive rights to a process developed by Dr. Hans H. Werner, an independent Canadian geologist. Various Polish groups are assisting Lynbar in commercializing Dr. Wer-
Solution mining heralded as most economical for potash "Solution mining is the most economical route to potash production," says Lynbar Mining Corp. president Bernard B. Jessel. The Toronto company is starting up a pilot plant this month near Duval, Sask., to recover potash by a solution mining technique which it has licensed. Meanwhile, a hundred miles to the southwest across Saskatchewan's rolling wheat fields, Kalium Chemicals, Ltd., gives tacit confirmation by expanding its 700,000 ton-peryear solution process mine by 50%. The Armour and PPG Industries joint venture expects the expansion to be completed early in 1969.
KaMum's potash storage bins Pure and white
ner's process. Lynbar is providing the pilot plant hardware and the Polish government will furnish technical personnel to operate it and evaluate commercial economics. Poland will then design and build a 1 million ton-peryear potash plant at Duval. Under a barter agreement, Lynbar will buy the plant from Poland, using muriate potash or cash as payment. The process should operate at $2.00 to $4.00 a ton less than existing potash mines, Lynbar says. For one thing, the firm says, the process eliminates one step of the above-ground refining procedure. For another, the lowtemperature process will use natural heat from underground thermal layers and will not have to generate additional heat, thus saving fuel costs. At least $15 million in capital investment will be saved because mild instead of stainless steel will be used. The lower temperature of the process permits this. Also, only a third to half as much machinery is needed for this process, Mr. Jessel says. Not only are capital costs cut in half compared to other processes, Lynbar says, but the cost of increasing capacity is much less. Solution mining is not new. The Chinese used it with bamboo pipes to obtain salt before the Christian era. Yet few technical details of the potash process have been disclosed. Kalium says its process, which came on stream late in 1964, is the first commercially successful potash solution mining process. Simply put, Kalium's process involves pumping a heated solution through bore holes into the potash beds about a mile below ground level. The solution, under pressure, dissolves the potash and is returned to the surface. The potash-rich liquors are purified in evaporators, thickeners, and crystallizers. The potash muriate is then dried to less than 0.1% moisture content. Solution mining gives a product of exceptional purity and white color, as contrasted with the pink of most North American potash, Kalium says; the process also allows for close control of particle size. Up to 40% of the potash ore is removed from the bed, Kalium says, compared with only 2 to 3 % removal by shaft mining techniques. At present, Saskatchewan produces 25% of the world's potash and is the leading exporter of the material. Although third in potash production this year (after the U.S. and U.S.S.R.), by 1972 Canada should be the world's largest producer of potash, IMC predicts. Current estimates indicate that there is enough potash under the wheatfields to supply the world's needs for at least 8000 years. DEC. 4, 1967 C&EN 23
