Of these changes, the flue modifications necessary to capture converter off-gases without excessive dilution can be quite expensive because the construction work has to be completed in an operating plant with minimal interference with plant pro- duction. Also, the addition of an acid plant substantially increases the power demand at a smelter. Currently, most smelters generate more than adequate power for their internal needs from the waste-heat boilers on the reverberatory furnaces and power generation can be increased by installing waste-heat boilers to cool the hot converter gases.
This increase in the power generation capacity is obtained at considerably higher capital cost as compared to the use of water sprays for converter gas cooling. Because there is considerable variation in the heat load at smaller smelters, the use of water sprays would be preferred.
The second approach for further reduction in emissions would be the one that would require the abandonment of green feed smelting and a reversion to concentrate roasting in conjunction with deep-bath smelting. New multiple-hearth roasters as well as fluid bed roasters can produce off-gases sufficiently high in SO? Of the three fluid bed roasters installed at copper smelters, the smallest unit has operated trouble-free for several years. The inter- mediate sized fluid bed unit has encountered considerable operating dif- ficulty in the past but these problems have been successfully overcome, and the management believes that they have sufficent in-house experience to properly design a new fluid bed roaster should they choose to do so.
The largest fluid bed roaster has also had considerable operating difficulties in the past but these seem to have been successfully overcome since the management of this particular company will rely on the fluid bed roaster as a part of its strategy to reduce sulfur oxide emissions at that partic- ular smelter.
In cases where the degree of sulfur elimination and iron oxidation in fluid bed roasting is not sufficient to substain an autogenous reaction, supplemental fuel can be burned in the roaster. This technology of burn- ing supplemental fuel has never been used in the operation of fluid bed roasters treating sulfide concentrates but only for the partial reduc- tion of iron ore by Montecatini in Italy. An alternative would be the utilization of multiple hearth roasters using supplemental fuel.
The usual way to charge hot calcines produced by roasting is by using Wagstaff guns. This method minimizes dusting problems when compared to roof charging of calcines and reduces the oxidation of calcines in the reverberatory furnace atmosphere. At plants currently using green feed smelting, the addition of roasters could be accomplished relatively easily, assuming that space restrictions are not very stringent within the plant. However, the change from green feed smelting using side charging to calcine smelting would require major modifications on the reverb.
These would be related to the change from dry hearth smelting to deep bath smelting and require, for example, the installation of cooling water jackets all around the crucible of the furnace. One copper producer undertook changes of this type several years ago, hence this approach appears to be technically feasible, though the costs would be highly variable since they would depend on the exact configuration of each reverb.
See an example of this, based on data from the McKee report, in Section J of this chapter. The advantages of roasting and calcine smelting are: reduction in fuel consumption in reverb and potential increase in plant throughput. The disadvantages are: introduction of large amounts of magnetite into the reverb and an increase in copper losses in slag resulting from higher matte grade.
In addition, for smelters equipped for roof charging of green concentrates, this would require essentially the rebuilding of the entire reverb complex and this might not be the most inexpensive strategy with respect to meeting the Federal ambient standards. The third approach which is being tested at present is based on the use of green feed smelting in closed-in reverbs and concentration of reverb off-gases using dimethylaniline DMA.
The advantages of this approach are the use of the green feed smelting concept which is easier from an operational viewpoint. The disadvantages are: DMA scrubbers have not operated on as large a scale previously and DMA scrubbing is a higher cost process when compared to roasting. In view of predicted increases in energy and fuel costs, the operating costs for this approach can also be expected to increase significantly in the future.
Of the approaches des- cribed in the previous section, electric furnace smelting has already been adapted and flash smelting is under serious consideration. Second Level Technology One of the major issues involved in the control of sulfur oxide emissions from non-ferrous smelters is the operational applicability of removal technologies to the smelters.
For example, Arthur G. McKee and Company, in a report on the National Air Pollution Control Adminis- tration PB stated that "only five control processes have been sufficiently tested and enough data made available so that costs can be estimated for their applicability to a range of smelter conditions. However, the Cominco absorption process was replaced by an Asarco developed absorp- tion process utilizing dimethylaniline DMA.
The major reason for the selection of DMA was the high sulfur dioxide recovery characteristics.
Although there was some disagreement between Fluor-Utah and McKee on the sulfur oxide removal capabilities of the Cominco ammonium sulfate process, there was no disagreement that both processes Cominco and DMA are high in capital and operating costs. Again, the two agreed that the capital and operating costs for sulfur production would be high. Each of the aforementioned processes results in a by-product which can be an item of commerce, i. The other sulfur oxides removal processes considered, i.
At the present time technology is only in the beginning of development, perhaps usable as a means of con- trolling emissions but crude and far from being optimized. At the present level of development, it appears that to use lime at reasonable circulation rates it is necessary to operate at low pH or to dilute the system with water. Both are undesirable, the latter particularly so because scrubber liquor must be drained to a water course, with accompanying water pollution, to make room for the water.
Consequently, the lime or limestone scrubbing process as well as the use of sodium hydroxide or sodium carbonate for scrubbing results in waste streams of solids or concentrated salt solutions which must be disposed of in a manner which will not pollute ground and surface waters. The problem of disposing of waste solids generated from scrubbing sulfur dioxide from gas streams or from neutralization of excess acid has been recognized by both the industries and regulatory agencies and is a prob- lem which must be considered for each individual plant location.
In general, where smelters are located near mines, the problem of disposal of solids generated in sulfur oxides removal is minimal because of the large amounts of solids already being disposed of in tailing piles. Furthermore, in the case of the copper industry particularly, arid to some extent in the lead and zinc industries, the problem of disposal of these solids is further decreased because of the aridity of the areas where the mines and smelters are located.
Within the present time constraints, the optimum strategy for the copper, lead and zinc industries is therefore based, in general. Since it is often possible to achieve Sulfur oxide removal from waste gases: Lime-limestone scrubbing tech- nology - A. Slack and H. Falkenberry, Tennessee Valley Authority and R. Harrington, Environmental Protection Agency.
Journal Air Pollution Control Assoc.
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This approach is based not only on the known operational dif- ficulties inherent in lime-limestone scrubbing but also on the fact that the lowest concentrations of sulfur oxides present in the major gas streams such as reverb off-gases are considerably greater than those that occur in, for example, the flue gases from fossil fuel power generating plants.
Some preliminary evidence indicates that scrubber efficiencies for these higher concentrated gases may be less than demonstrated on power plant flue gases. Also, the variable flows that occur in smelters have caused some of the preliminary designs to be limited to less than , SCFM units; however, single train scrubbing units of larger capacity are available which would probably result in lower capital investments than often estimated. However, because'these scrubbers have not been installed and operated for long periods of time, it is not surprising to find a reluctance to consider them when confronted with a relatively short time period for installation of equipment for compliance with emission regu- lations.
Therefore, the principal control methods being considered by the industries are toward the removal of sulfur oxides as sulfuric acid; liquid sulfur dioxide with scrubbing being considered principally for those gas streams of low sulfur oxides concentration, i. As higher and higher degrees of sulfur recovery are considered, "converter aisle losses" become increasingly important. These low level emissions are difficult to quantify since they would have to be calculated by difference and their magnitude is not known at the present time with any degree of certainty.
Because the ambient SOx concentrations are affected by local weather patterns, tall stacks, use of dilution air, etc. It is however possible to calculate the costs associated with different degrees of emission control since each type of technology can be the opti- mum within a particular range of emission control objectives. We have prepared Figure III-l in order to show the costs associated with different degrees of emission control.
The figure is based on the sequential selection of emission control strategy. We have selected collection of converter gases and acid manufacture as the basic strategy Technology A since these gases are a major source of SOx emissions that can be obtained in adequate concentrations for acid manufacture. Also, all the western copper smelters have pollution abatement plans that include this approach. The cost range denoted by this bar is the range of total costs i. However, since the purpose of this exercise is to show what level of emis- sion control can be obtained at what cost, each technology would logically be utilized to its limit and we believe that the use of horizontal bar representation of cost vs.
We have selected roasting of concentrates Technology B as the second strategy.
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For example, Model B in the McKee report was based on this approach but incorporated the use of dilution air for cooling of converter gases. A variety of decision paths are possible and we have chosen such removal technologies as lime-limestone scrubbing or DMA absorption with recovery of liquid sulfur dioxide for sale or for additional acid production as representative of Technology C.
Since these technologies do not as yet have a firm basis for detailed engineering and operating costs, their application to any specific smelter would result in a wide variation of costs as shown by the bar for Technology A plus C. This technology, labelled D, would be expected to have even higher costs and variability from smelter to smelter and the total cost is shown as Technology A plus D. To show approximately the rapid increase in costs of sulfur removal as higher and higher percentage recoveries are required, the dotted line of Figure III-l connecting the mid-points of the estimated ranges has been drawn.
This line is characteristic of operating processes as higher and higher recovery efficiencies are required while reflecting the variability that exists between smelter locations. In controlling water pollution it is often necessary to remember that in con- trolling the air pollution problems, a water pollution problem can be cre- ated since some of the most effective air pollution technologies are based on the use of water in scrubbing.
Furthermore, the water drainage problem from mines and tailings disposal areas is of considerable concern to the industries, but, of course, much less than in the coal mining industry.
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Although air and water pollution control have been considered separately, it is mandatory that in arriving at solutions to one problem, another one of equal or greater magnitude is not created. However, in certain instances the chemical additives used in ore beneficiation can contribute to nutrient enrichment of receiving waters so that algal growth, for example, is accelerated in holding ponds. Nevertheless, the technology required for wastewater treatment is principally that required for removal of suspended solids and the removal of soluble metals since many of the latter have known toxic effects in the aquatic environment.
Since the industries must deal with complex minerals containing many minor metals in addition to the major ones of copper, lead and zinc, the wastewater treatment problems become increas- ingly significant and difficult to treat as the concentrations of metals such as cadmium, mercury, chromium, arsenic, nickel and so on increase.
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In general the present wastewater treatment technology is based on separ- ation of suspended solids followed by lime treatment to a pH sufficiently on the alkaline side to precipitate metallic elements as hydroxides which have generally low solubilities. The precipitated solids are removed in settling tanks or allowed to settle out in ponds.
The metal values in the precipitated solids may be recovered if in high concentrations or the solids are buried or placed in holding ponds or tailing piles. The alka- line waters can then be neutralized to a pH acceptable for discharge or reuse.
Secular variations in thunder‐day frequencies in the twentieth century
At this point the treated waters will still contain metals equal to or greater than the solubilities of the precipitated forms. In general these concentrations are greater than theoretical due generally to incom- plete reactions, carryover of colloidal particulates, pH fluctuations and the effects of other ions in solution. Consequently, precipitation-type treatment systems, while effective, are limited by a number of physico- chemical laws and if the permissible concentrations of heavy metals are established at values lower than these limits, other and more costly treatment methods would be required.
Among the latter are ion-exchange, evaporation, electrodialysis, and reverse osmosis. The water pollution control problems within the industries are especially dependent upon plant, and mine location, i. These procedures are well known throughout the field of wastewater treatment; however, the major considerations will revolve, undoubtedly, around the questions of water availability, value of materials, and the currently unde- fined water discharge standards.
Domestic a. Introduction The United States has been the largest copper producing country in the world since before the turn of the century. The domestic primary copper industry is composed of approximately firms engaged in producing and selling copper. The major producers are vertically integrated and have mining, smelting, refining, fabricating, and marketing interests. Other large producers mine and have processing facilities through the smelting or refining stages, and many companies mine and concentrate their ores and ship the product to custom plants for smelting and refining.