Section 6. Case Studies 6 CASE STUDIES (a) Platinum Group Metals in Urban Environment (b) Sustainable Urban Drainage (c) Artisanal activities in Vicenza, Northern Italy (d) Pharmaceuticals in the Urban Environment (e) Personal Care Products, Fragrances in Urban Waste Water and Sewage Sludge (f) Surfactants in Urban Wastewaters and Sewage Sludge (g) Use of Polyelectrolytes; The Acrylamide Monomer in Water Treatment (h) Landfill leachate (i) Potentially Toxic Elements (PTE) transfers to Sewage Sludge (j) Effect of Chemical Phosphate Removal on PTE Content in Sludge 113 Section 6. Case Studies (a) Platinum Group Metals in the Urban Environment Introduction The platinum group of metals (PGMs), sometimes referred to as the platinum group elements (PGEs), comprise the rare metals platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os) and are naturally present in a few parts per billion (mg/kg) in the earth’s crust. The elements are noble chemically unreactive metals, and are found in nature as native alloys, consisting mainly of platinum. Recently these metals have gained importance as industrial catalysts including vehicle exhaust catalysts (VECs). This use and possible implications for human health were the subject of an earlier review undertaken by Imperial College, London for the UK Department of the Environment (Farago et al, 1995; 1996). Increasing understanding of the environmental damage of vehicle emissions has led to the introduction of stringent emission control standards throughout the western world. Since 1974 all new cars imported or produced in the United States have had catalytic convertors fitted, cutting down hydrocarbon and carbon monoxide emissions. In 1977 they were fitted to a substantial proportion of all cars sold in America, where at the time, this application accounted for 32% of the total Pt usage (Herbert, et al., 1980). Vehicle exhaust catalysts have also been used in Japan since 1974. Vehicle exhaust catalysts were also introduced in Germany in 1985, in Australia in 1986, and into the UK at the beginning of 1993 in response to the emission standards equivalent to the US standards which were introduced in the EC at that time. Other uses of PGMs are noted in later sections. Sources The PGMs are found in nickel, copper and iron sulphide seams (Bradford, 1988). They are currently mined in South Africa, Siberia and Sudbury, Ontario. World mine production of the PGMs, of which 40-50% is platinum, has steadily increased since 1970. This reflects the increasing world-wide use of PGM vehicle catalysts (IPCS, 1991). From 1988-1992 world mine production was essentially constant at around 255 tonnes per year (WMS, 1994). The amount of PGMs present in the earth’s crust down to a depth of 5km, and hence technologically attainable, are still enormous when compared with present requirements, but only a fraction of the pertinent ores is sufficiently rich for commercial exploitation. Of the total of 3x1011 tonnes of PGMs in the earth’s crust, 3x103 tonnes have been mined, and 7x1010 tonnes are minable (Renner and Schmuckler, 1991). The total worldwide supply of Pt for 1999 and 2000 was 138 tonnes and 153 tonnes respectively for Pd 230 tonnes and 224 tonnes respectively, and for Rh 14.2 tonnes and 20.9 tonnes respectively (Johnson Matthey, 2000) Uses of platinum group metals. By far the greatest use of PGMs both in Europe and worldwide is in vehicle catalysts, with additional major uses in the chemical industry, electrical and electronics industries, petroleum industry, the manufacture of jewellery, as a cancer treating drug in medicine, as alloys in dentistry and in the glass industry. Demands by application for 1999 and 2000 for PGMs are shown in Table a.1. (Johnson Matthey, 2000) 114 Section 6. Case Studies TABLE a.1 Platinum Group Metals Demand by Application (Worldwide) Application kg 1999 (kg) 2000 (kg) PLATINUM Autocatalysts: gross 45600 51000 Autocatalysts: recovery -12000 -13000 Jewellery 79400 83300 Industrial 38400 41400 Investment 5100 -1420 Total Demand (Pt) 159000 146000 PALLADIUM Autocatalysts: gross 166700 146000 Autocatalysts: recovery -5530 -6520 Dental 31500 24700 Electronics 56100 58600 Other 16600 15000 Total Demand (Pd) 265000 238000 RHODIUM Autocatalysts: gross 14400 16000 Autocatalysts: recovery -1870 -2240 Chemical 964 992 Electronics 170 170 Glass 851 1050 Other 312 312 Total Demand (Rh) 14900 16200 RUTHENIUM Chemical 2440 1930 Electrochemical 2040 2270 Electronics 5560 6580 Other 1160 1360 Total Demand (Ru) 11200 12100 IRIDIUM Automotive 964 397 Chemical 198 170 Electrochemical 794 680 Other 936 1450 Total Demand (Ir) 2890 2690 115 Section 6. Case Studies Trends over time in platinum and palladium uses by application for Europe are shown in Table a.2 and a.3. TABLE a.2 Platinum demand by application in Europe (kg) Platinum demand 1992 (kg) 1994 (kg) 1996 (kg) 1998 (kg) 2000 (kg) Autocatalyst: gross 16300 17200 14600 15500 17900 Autocatalyst:recovery -142 -284 -567 -851 -1130 Chemical 1420 1420 1700 1700 2410 Electrical 851 709 709 1280 2270 Glass 425 851 1130 709 709 Investment:small 992 1276 142 142 0 Jewellery 2410 2840 3540 4540 5670 Petroleum 567 709 425 425 284 Other 1560 1840 2130 2410 2840 Totals (Pt) 24400 26500 23800 25800 30900 TABLE a.3 Palladium demand by application in Europe (kg) Palladium demand 1992 (kg) 1994 (kg) 1996 (kg) 1998 (kg) 2000 (kg) Autocatalyst: gross 1130 7370 24400 38800 51600 Autocatalyst:recovery 0 0 142 -142 -425 Chemical 2100 1700 1840 1840 2690 Dental 8500 7230 7230 5950 3120 Electronics 5950 7230 8500 7660 7370 Jewellery 992 851 851 1420 1280 Other 425 709 567 709 567 Totals (Pd) 19100 25100 43200 56300 66200 Of particular interest is the increased demand for palladium in Europe, largely in response to the introduction of Euro Stage III legislation from January 2000; palladium – rich catalysts will meet stricter emission limits for petrol models, resulting in a further move away from platinum technology (Johnson Matthey 2000). Catalytic convertors A catalytic converter is a unit about the size of a small silencer that fits into the exhaust system of a car. The metal catalyst is supported on a ceramic honeycomb monolith and housed in a stainless steel box similar in shape to that of a conventional silencer. About 1-3g of PGM is contained in some vehicle exhaust catalysts, approximately 50g of PGM per cubic foot of catalyst (Steger, 1994). Due to the commercial sensitivity of these products it is difficult to obtain data on the exact amounts in each of the many different formulations of catalyst. The honeycomb made of cordierite contains 300 to 400 square channels per square inch (6.45cm2), and is coated with an activated high surface area alumina layer called the washcoat (Farruato, 1992) containing small amounts of the precious metals, platinum, palladium and rhodium in varying proportions. The conventional three-way catalysts typically contain 0.08% platinum, 0.04% palladium and 0.005-007% rhodium (Hoffman, 1989). These metals convert over 90 percent of carbon monoxide (CO), hydrocarbons (HC) and nitrous oxides (NOx) into carbon dioxide (CO2), water (H 2 O) and nitrogen (N2). Platinum is an effective oxidation catalyst for carbon monoxide and hydrocarbons, but it is more sensitive to poisoning than palladium and so can only be used in cars which use unleaded petrol. Palladium is becoming increasingly used instead of platinum due to the higher costs of the latter. The rhodium oxidises the hydrocarbons and reduces the NOx emissions. Base 116 Section 6. Case Studies metals are also incorporated, cerium being the most frequently used; others include calcium, strontium, barium and iron. Chemical fingerprinting of ground autocatalyst materials has been undertaken by laser ablation and analysis by ICP-MS for 31 elements (Rauch et al, 2000). Variations in composition were found to occur in agreement with the known fact that variations occur from one manufacturer to another and from one year to another. An association between PGMs and Ce in road sediments was ascribed to the emission of PGMs as abraded washcoat particles onto which PGMs are bound and of which Ce is a major component. Recycling Of the total platinum consumption in the United States, approximately thirty per cent is accounted for by vehicle catalysts (IPCS, 1991). The recovery of spent autocatalysts from vehicles at the end of their lives is regarded as important and substantial secondary sources of platinum as well as palladium and rhodium (Torma and Gundiler, 1989). The quantity of spent autocatalysts greatly increased in the United States from 1984 to 1988. These scrapped autocatalysts present an important secondary source of the platinum group metals. On current projections it is expected that 3.5 million catalysts will be available for recycling in the UK by 2000. Platinum group metals in the environment. The average concentration of platinum group metals in the lithosphere is estimated to be in the region of 0.001-0.005 mg.kg-1 for Pt, 0.015 mg.kg-1 for Pd, 0.0001 mg.kg-1 for Rh, 0.0001 mg.kg-1 for Ru, 0.005 mg.kg-1 for Os and 0.001 mg.kg-1 for Ir (Greenwood and Earnshaw, 1984). Although a rapid increase in Pd in sediments from the Palace Moat, Tokyo, Japan was reported by Lee (1983) between 1948 and 1973, it seems unlikely that this was connected with car catalytic convertors since there were few in use in Tokyo by 1973. Concentrations of Pt and Pd in Boston Harbour have been investigated to evaluate Pt and Pd accumulation and behaviour in urban coastal sediments (Tuit et al, 2000). Increased levels of both metal of approximately 5 times above background concentrations were ascribed to anthropogenic activity with catalytic convertors a major source. It was concluded that anthropogenic enrichments can significantly influence coastal marine inventories of PGMs.