United States Environmental Protection Agency Industrial Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-83-120 July 1984 Project Summary Process Modifications Toward Minimization of Environmental Pollutants in the Chemical Processing Industry L.L Tavlarides Eight industries employing chemical processes were surveyed to develop a matrix of significant pollution problems and attendant process modifications which would have an impact on the reduction or elimination of generic pollutants shared by the eight diverse process industries surveyed: non- ferrous metals refining, electroplating, coal conversion, specialty chemical, iron and steel, paper and pulp, primary aluminum, and phosphate fertilizer. The study concluded that the follow- ing areas of research are the most promising for minimizing pollutants from the industries surveyed: solvent extraction, catalyst deactivation, leach- ing, gas absorption and gas-liquid-solid reactions. This Project Summary was developed by EPA's Industrial Environmental Research Laboratory, Cincinnati, OH. to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction This planning project suggests funda- mental research studies which could result in the reduction of industrial pollutants in the chemical process industry. Eight industries are surveyed to develop a matrix of significant pollution problems and attendant process modifi- cations which would effect the reduction. The eight industries are listed below. 1. Refining of nonferrous metals 2. The electroplating industry 3. Coal conversion processes 4. Specialty chemicals 5. The iron and steel industry 6. The paper and pulp industry 7. The primary aluminum industry 8. Phosphate fertilizer industry These diverse industries showed generic pollution problems; the study identifies process pollution modification strategies which are also generic in nature. Refining of Nonferrous Metals Introduction This chapter concentrates on the refin- ing of nonferrous metals from mineral ore by three processes: 1. Copper production by pyrometallur- gical processes 2. Copper production by hydrometallur- gical processes 3. Uranium production by hydrometal- lurgical processes. Copper Production by Pyro- metallurgical Processes The following areas are recommended for further research: • Optimization of the communition of dry mineral ore to redu,ce the amount of water used in froth flotation • Recover value-bearing products by dissolving the metals from particulates collected in the electrostatic precipi- tators and use solvent extraction procedures to extract the desired products • Use solvent extraction to recover copper or other metals from effluent ------- streams before the water is sent to the tailing ponds • Improve smelter design to contain and eliminate the release of SC>2 and other hazardous flue gases into the atmosphere. Copper Production by Hydrometallurgical Processes The following areas are recommended for further research: • Recover trace metals in the effluent streams by using solvent extraction. Conduct research in the area of simultaneous extraction of several metals that are considered hazardous pollutants. • Recover entrained solvents by filtra- tion, flotation, centrifugal separation, etc. Study the various methods of separating liquid-liquid mixtures and determine the best process to use. • Solvents tend to degrade due to temperature, pH, or radiation ex- tremes. Analyze the byproducts of this degradation and determine the best way to eliminate these byproducts either in the recycle stream or the exit stream. • Evaluate new techniques for leaching sulphide ores or develop new tech- niques to improve selectivity in leaching mineral ores. Uranium Production by Hydrometallurgical Processes The following areas are recommended for further research: • Evaluate new leaching solutions that may offer improvement in leaching selectivity and/or efficiency. • Determine the best solvent for solvent extraction of uranium salts with minimal degradation. • Divert recycle streams into additional process circuits to remove trace metals. Electroplating of Common Metals Electroplating is a series of process steps that involves the preparation of the part in addition to the plating operation. The sequence and/or the process steps may vary from plant to plant because of the many variables involved with electro- plating. There are numerous methods of treat- ment for dissolved materials that exist in effluent streams. They include substitu- tion of low concentration solutions in place of high concentration baths; use of non-cyanide solutions in place of the cyanide treatments; use counter-flow rinses; adding a wetting agent to rinse waters; installing air or ultrasonic agitation; recovery and reuse of metals in effluent streams by solvent extraction; and recycling used rinse waters into the make-up solutions of their respective treating baths. Each method has advantages and dis- advantages that must be considered with respect to the specific electroplating industry Coal Conversion Processes The unpredictability of the international energy market and the very real danger of global oil shortages in the next few decades have necessitated a rapid expansion in the domestic energy base in the U.S. Consequently, the commercial production of synthetic fuels from the abundant reserves of coal is a major objective of the nation's energy research and development programs. Coal lique- faction and coal gasification technologies have received renewed interest in this regard. Economic viability and environ- mental impact will be the limiting factors in the commercialization of such process- es. Lurgi Coal Gasification Process The following areas are recommended for further research: • Stabilization of gasifier and boiler ash to decrease or prevent leachabil- ity. • Operating data and composition on spent methanation guard, shift and methanation catalyst to determine possible extraction of valuable and toxic metals. • Studies on the use of spent methana- tion catalyst as sulfur guard. • Development of solvent extraction systems to remove non-phenolic organics and determination of distri- bution coefficients for existing sol- vents. • Engineering data on various sulfur recovery, SC>2 and tail gas pretreat- ment processes. SRC Coal Liquefaction Process The following areas are recommended for further research: • The applicability of electrostatic and magnetic filters to control emissions of coal dust particles in the submicron range. • Leachability of gasifier slag and fly ash to determine treatment and/or disposal methods. • Extraction of valuable metals (Ni, Co, Mo, etc.) from spent shift and hydrogen generation catalysts. • Studies on the absorption of SOx and CC"2 in Stretford process leading to process modification to reduce CO2 emissions in tail gas. • Modification of steam generation operation to reduce NO* emissions. Explosives Industry The processes involved in manufactur- ing of high explosives are discussed in the final report. The purpose of the discus- sion is to provide an insight into process modification as a method to reduce pollutants arising from these processes. The final report discussion includes the two most produced high explosives, trinitrotoluene and nitrocellulose. Both explosives are generated by nitration processes to yield nitrocompounds. TNT Product/on The following areas are recommended for further research: • Research on kinetics of the nitration reactions which will permit alleviation of pollutants by adoption of a low- temperature denitration stage. • Material balances to find the optimal design for the fume recovery system in the nitration-separation process. • Recovery of TNT in the "pink water" by application of foam separation to an aqueous solution. Nitric Acid Production The following areas are recommended for further research: • Studies on kinetics and mass transfer process for heterogeneous catalysis to improve the catalytic bed design which will reduce NO dissociation and increase NHs consumption. • Studies on heat and mass transfer with reaction in absorption towers to optimize HNOa production by finding the optimal parameters for adsorp- tion tower operation. • Consideration of nitric acid produc- tion by means of a super azeotropic mixture which may be useful in modification of the present process. Nitrocellulose Production The following areas are recommended for further research: • Better understanding of the kinetics of the cellulose nitration will indicate methods of operation to minimize NOx and SOx formation. • Better understanding of absorption of SO, and addition of an absorption tower to the acid concentrator to recover NOX. ------- • Research on filtration operations and filtration units for effective recovery of NC fines from boiling tub, Jordan beater and poacher houses. • Reexamine and modify flow streams to optimize water usage by recycle and other techniques in the purifica- tion process. Iron and Steel Industry The manufacture of steel involves many processes which require large quantities of raw materials and other resources. Due to the wide variety of products and processes, operations vary from plant to plant. However, the steel industry can be segregated into two major components; raw steel making, and forming and finishing operations. An overview of the iron and steel process is given in the final report and is summarized here. In the first major process, coal is converted to coke. Nearly all active coke plants are byproduct plants which pro- duce, in addition to coke, byproducts such as coke oven gas, coal tar, crude or refined light oils, ammonium sutfate or anhydrous ammonia, and napthalene. Less than 1% of domestic coke is produced in beehive coke making. The coke from coke making operations is then supplied to the blast furance pro- cess where molten iron is produced. In the blast furnace, iron ore, limestone and coke are placed into the top of the furnace and air is blown countercurrently from the bottom. The combustion of coke provides heat which produces metallurgi- cal reactions. The limestone forms a fluid slag which combines with unwanted im- purities in the ore. Molten iron from the bottom of the furnace and molten slag, which floats on top of the iron, are period- ically withdrawn. Iron and Steel Industry The following areas are recommended for further research: • Use of refined or cleaned coal in coke making. • Study of the formation of cyanides and carbonyls during coking in order to prevent or reduce pollutant for- mation. • Dry coke quenching of U.S. coals to eliminate quench water contamina- tion. • The effect of process variables such as coal grinding and coking time on coke produced. This information would be used to improve the quality of coke stability in order to enhance blast furnace performance. • Development of biological oxidation systems to remove HCN from bypro- duct coke making wastewaters. • Absorption of H2S from coke oven gases by Glaus or Stretford process. • Development of better CN removal systems from blast furnace waste- waters by using additives such as Caros acid (H2SOs) and polyphosphate, and by aeration. • Optimization of pH and contact time to improve alkaline chlorination and ozonation to upgrade blast furnace wastewaters. • Solvent extraction of zinc or dezinci- fication by Walez process to remove zinc from blast furnace dusts. Such zinc removal can facilitate the use of treated dusts in the sintering process. • Study of kinetics of H2S and SO2 formation during blast furnace slag quenching to develop methods by which H2S formation can be de- creased. • Study the kinetics of formation and oxidation of cyanides in the blast furnace to optimize the design and operation of the stack in order to oxidize the cyanide. • Development of solvent extraction and sulfide precipitation methods to remove toxic metals from the recycled steel plant wastewaters. • Study the effect of temperature and agitation in order to optimize pickling operations. Paper and Pulp Industry The pulping process, kraft (or sulfate) pulping in particular, is fully discussed in the final report. Pulping wood is an initial process in the manufacture of paper and paper products. The pulping process consists of conversion of fibrous raw material, wood, into a material suitable for use in paper, paperboard, and building materials. Pulp is the fibrous material ready to be made into paper. There are four major chemical pulping techniques: (1) kraft or sulfate, (2) sulfite, (3) semichemical, and (4) soda. Of the major pulping techniques, the kraft or sulfate process produces over 80% of the chemical pulp produced annually in the United States. In 1970, there were 116 mills producing 29.6 million tons of pulp by the kraft process. During the same year, the pulp and paper board consump- tion was 56.8 million tons. Paper and Pulp Industry The following areas are recommended for further research: • Research on digestion of wood chips to determine optimal sulfidity, pH, and temperature to reduce pollution. • Studies on control of fiber carryover from the blow tank by cyclone and/or reduction of relief pressure and selection of wood-to-liquor ratio to prevent TRS emission. • Comparative studies on design and application of diffusion and displace- ment washers to minimize TRS. • Effect of black liquor oxidation and pH control on weak and strong black liquor to reduce TRS emission. • Studies on the direct and non- contact evaporation in the recovery furnace system to determine capabil- ity and merits of each unit in reducing the TRS emission. • Research on combustion of strong black liquor to prevent black out conditions and stick dust formation by optimizing the design and opera- ting conditions in the recovery furnace. • Research and application of scrub- bing techniques to reduce TRS emission. The Primary Aluminum Industry The primary aluminum industry consists of processing bauxite ore to produce alumina (and occasionally aluminum hydroxide) and processing the alumina to produce aluminum. Approximately, 7.6 x 106 tons of alumina were produced in U.S. from processing about 15.4 x 106 tons of bauxite in 1972, 94% of the alumina was utilized to make aluminum. Primary Aluminum Industry The following areas are recommended for further research: • Leaching and extraction of red mud to recover mineral values. • Improving the mechanical strength, adsorption capacity and particle size distribution of calcined alumina by optimizing precipitation and calcina- tion of alumina. • Optimizing the temperature for and stripping of high silica U.S. Bauxite ores. • Enrichment of high silica U.S. Bauxite using bacterial action. • Improving calcination of AI2O3 to reduce its moisture content, thereby reducing formation of HF from electrolytic cells. • Optimization of the cryolite bath (NaF/AIF3) ratio, alumina content and temperature of cell to reduce flouride emissions. • Increasing the adsorption capacity of AbOs to remove HF in the fumes from electrolysis. ------- • Understanding the interaction of HF and S0« on AI203 to improve dry scrubbing of SO* gases from the electrolytic cell. • The effect of various additives in removing sulfur in coal as slag. • Effect of adding lithium on cell operating temperature and HF emis- sions. • Leaching of cathode linings to remove flourides and cyanides. Phosphate Fertilizer Industry Fertilizers in general can be categorized by their composition of plant nutrients. The fertilizers differ in their composition of plant nutrients of nitrogen, phospho- rous, and potassium. Normal superphos- phate contains only one nutrient, phos- phorous. Generally, the solid and liquid mix fertilizers contain all three nutrients in varying amounts. Over 44 million metric tons of phos- phate rock were mined in the United States during 1975. Approximately 22.75 million metric tons were consumed by the fertilizer industry during the same period. The phosphate based fertilizers are produced by conversion of unsoluble phosphate ore into the soluble form necessary for plant consumption. The phosphoric acid, backbone of phosphate fertilizer, is formed by mixing phosphate rock with sulfuric acid. The final report fully describes the effect of concentrates on the production of phosphoric acid, normal superphos- phate, and ammonium phosphate. Wet Process Phosphoric Acid Production The following areas are recommended for further research: • Studies on purification of phosphate feed to reactor to reduce impurities which cause byproduct formation. • Comparative studies on adsorption and absorption of flourme to deter- mine the most efficient technique to alleviate flourine emission. • Research on the design and opera- ting parameters of the scrubber to reduce plugging and increase the rate of flourine transfer from the vent gases to scrubbing medium. Ammonium Phosphate Production The following areas are recommended for further research: • Research on kinetics of reaction of ammonia with phosphoric acid to enhance this reaction, either cataly- tically or by increasing the residence time in the reactor vessel, which would reduce the emission. • Studies on design of the reactor vessel and granulators to minimize the ventilation rate which would lead to smaller volumes of gaseous emis- sion. • Research on the design and selection of optimal operating parameters for the scrubbing unit to reduce the ammonia, flouride, and particulate emissions. Superphosphate Production The following area is recommended for further research: • Studies on the scrubber design and optimal operating parameters to reduce flourine emissions. Conclusions and Recommendations This project identified the following areas of research as most promising for minimizing pollutants from eight chemical processing industries studied. Solvent Extraction Modification of solvent extractor designs and operations should minimize metal ions or non-phenolic organics in process streams leaving extractor batteries in hydrometallurgical and coal liquefac- tion processes, respectively. Studies could include modelling of selective ion extraction in multiple metal systems, characterization of liquid dispersion properties such as surface area and droplet mixing as a function of power consumption, extraction kinetics, and separation of liquid-liquid dispersions. Catalyst Deactivation Modification of catalyst reactor bed operation and studies on catalyst deactiva- tion will increase catalyst life and reduce the volume of spent catalyst from coal gasification operations. Studies could include modelling catalyst deactivation phenomena as affected by temperature, pressure, feed gas composition, catalyst structure, and catalyst type. Optimal reactor operation studies for sulfur guard catalysts (ZnO), shift catalysts (cobalt- molybdate), and methanation catalysts (nickel) can be conducted. Leaching Processes Modification and improvement of leaching processes for sulfide or oxide ores will reduce ground water contami- nation and dissolved metal salts in process streams in hydrometallurgical processes. These results also apply to recovery of metals from particulates (smelting dust), coal liquefaction ash, spent catalysts in coal gasification, and coal liquefaction residues. Studies could include vat leaching using ammonial or in organic acid solutions. Characterization of kinetics of leaching as affected by particle size, temperature, concentra- tions and particle structure can be explored. Minimum power requirements to suspend particles and maximize particle-liquid mass transfer can be studied. Gas Absorption Modification and improvement of gas absorption processes such as the Stret- ford absorption process will reduce emissions of Hz, HCN, and CO2 in tail gases from coal liquefaction processes and H2S and S02 for smelter off gas recovery operations. Studies could include gas-liquid mass transfer and gas- liquid reactions in absorption liquids (sodium metavanadate, sodium carbo- nate, sodium bicarbonate, and ADA) as affeced by temperature, pressure, and gas-liquid contacting. Gas-Liquid-Solid Reactions Modification and improvement of reactors for contacting and reacting gas- liquid-solid dispersions would minimize particulate emissions in coal liquefaction reactions as well as vat leaching process- es. Studies could include coal dissolution rates, gas dispersion, particulate agglom- eration, dissolved gas-particle reactions, and determination of the rate limiting steps as affected by mechanical agitation, temperature, pressure and compositions. ------- L. L Tavlarides is with the Illinois Institute of Technology. Chicago, IL 6O616. W. A. Cawley is the EPA Project Officer (see below). The complete report, entitled "Process Modifications Toward Minimization of Environmental Pollutants in the Chemical Processing Industry," (Order No. PB 84-133 347; Cost: $17.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Industrial Environmental Research Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 •USGPO: 1984-759-102-10613 ------- United States Center for Environmental Research Environmental Protection Information Agency Cincinnati OH 45268 Official Business Penalty for Private Use S300 * ------- |