text: The commercial development of the Cell occurred indirectly as a result of problems being experienced in MIMs Mount Isa lead–zinc concentrator (sometimes referred to as a "mill" in the mining industry). MIM had been operating a lead–zinc concentrator at Mount Isa since 1931, although lead–zinc ore was substituted with copper ore for a time between mid-1943 and mid-1946. Over time, the lead, zinc and other mineral grains in the ore became progressively finer, the ore grade decreased and it became more difficult to treat. These trends, combined with an increase in the concentrators throughput, significantly reduced the concentrator's performance in the 1980s, resulting in a "tense" period of "an endless circle of circuit changes, reagent changes, operator changes, metallurgist changes, and so on". The decreasing grain size and pushing the grinding circuit beyond its design throughput meant a reduction in the degree of separation of the individual mineral grains (referred to as "liberation") during grinding. From 1984 to 1991, the liberation of sphalerite (the zinc-bearing mineral, ZnS) decreased from almost 70% to just over 50%. This decrease in liberation resulted in a reduction in the recovery of zinc to saleable zinc concentrate.
  The initial response to the problem of decreased zinc recovery was in 1986 to start to produce a lower-grade concentrate that was a mixture of zinc and lead (known in the industry as a "bulk concentrate" and referred to at Mount Isa as the "low-grade middlings concentrate"). This concentrate typically contained 34% zinc and 13% lead, compared to the normal zinc concentrate composition of at least 50% zinc and less than 3% lead.
  By producing the bulk concentrate, the total recovery of zinc for sale was maintained at over 70% until 1989. However, the high lead content meant that the bulk concentrate could not be treated by the electrolytic zinc process, and it had to be sold to zinc smelters using the more-expensive Imperial Smelting Process. Initially, MIM received good revenue from its bulk concentrate, but as the nature of the ore continued to deteriorate, the production of the bulk concentrate increased and saturated the market. Payment terms declined until MIM received less than half the payment for zinc in the bulk concentrate than it received for zinc in the zinc concentrate.
  The problems in the concentrator also affected the performance of MIMs Mount Isa lead smelter. The lead–zinc ore also contained increasing amounts of fine-grained, carbonaceous pyrite (FeS). This material was naturally hydrophobic and floated without the aid of a collector into the lead concentrate, diluting it. The additional sulfur from the pyrite in the lead concentrate reduced the lead smelters lead production because the ability to eliminate sulfur from the concentrate was lead smelter's capacity bottleneck.
  As part of the effort to try to fix the problems, MIM installed some column flotation cells in the zinc concentrate and bulk concentrate sections of the plant. In those days, the air was introduced into flotation columns using air spargers, usually in the form of a bag or sheath around a pipe. The spargers were high-maintenance items, and their performance was critical to the operation of the column.