Environmental Chemistry IB Option E Part 4: Soil & Waste.
Post on 26-Dec-2015
Slide 1 Environmental Chemistry IB Option E Part 4: Soil & Waste Slide 2 Soil Degradation Soil quality has been altered in such a way that it lowers crop production. Can be caused by changing weather patterns, or by anthropogenic factors such as acidification contamination erosion salinization from industrialization, irrigation, overgrazing, overharvesting of trees Slide 3 Salinization from constant or excess irrigation. Salts from irrigated water accumulate in soil long after the water evaporates. Plants die from toxic levels of salt or inability to take up water from salty soil with their roots. Slide 4 Nutrient depletion intensive farming no time for fields to be fallow; no organic fertilizers used Slide 5 Soil pollution can be caused by industrial discharge use of pesticides and fertilizers illegal dumping of spent engine oil, etc. all lead to groundwater pollution. Slide 6 Soil Organic Matter (SOM) organic constituents of the soil Biological humus provides source of energy and source of essential nutrient elements nitrogen, phosphorus and sulfur to sustain healthy growth. Slide 7 Soil Organic Matter (SOM) organic constituents of the soil Physical humus helps soil retain moisture; dark color of humus absorbs heat. Slide 8 Soil Organic Matter (SOM) organic constituents of the soil Chemical humus acts like clay with its cation exchange capacity. Contains active sites which enable it to bind to nutrient cations. Also acts as acid-base buffer. Slide 9 Common organic soil pollutants Hydrocarbons and other VOCs Pesticides, herbicides & fungicides Polyaromatic hydrocarbons (PAHs) Polychlorinated biphenyls (PCBs) Slide 10 Slide 11 Table 7: Methods of Waste Disposal MethodAdvantagesDisadvantages Landfill Efficient method to deal with large volumes Filled land can be used for building or other community purposes Local residents may object to new sites Once filled, needs time to settle, and may require maintenance as methane released Open Dumping Inexpensive Convenient (for the dumper) Causes air and ground water pollution Health hazard: encourages rodents and insects Unsightly Ocean Dumping Source of nutrients Convenient and inexpensive Danger to marine animals Pollutes the sea Incineration Reduces volume Requires minimal space Produces stable, odor-free residue Can be used as a source of energy Expensive to build and operate Can cause pollutants, e.g. dioxins, if inefficiently burned Requires energy RecyclingProvides a sustainable environmentExpensive Difficulty in separating different materials; not possible in all cases Slide 12 Table 8: Recycling MaterialDescriptionComments Metals Mainly aluminum and steel. The metal are sorted, then melted and either reused directly or added to the purification stage of metals formed from their ores Particularly important for metals such as aluminum, which require large amounts of energy to produce directly from ore Paper Taken to the plant, sorted in grades. Washed to remove inks, etc., made into a slurry to form new types of paper, such as newspaper and toilet rolls. Energy required to transport. Composting may be as efficient. Glass Sorted by color, washed, crushed, then melted and molded into new products Glass is not degraded during the recycling process, so can be recycled many times PlasticsIndustrial plastic is already sorted, but household waste plastic must first be sorted. Degraded to monomers by pyrolysis, hydrogenation, gasification, and thermal cracking, then repolymerized Fewer pollutants formed, and energy used to recycle rather than to make from crude oil. Better to reuse than to recycle. Slide 13 Table 9: Plastics Recycling Codes (no need to memorize, just an FYI item) Code Symbol Abbrev.NameTypical Use 1PETPolyethylene terephthalateFizzy drink bottles and oven-ready meal trays 2HDPEHigh-density polyethyleneBottles for milk and washing-up liquids 3PVCPolyvinyl chloride Food trays, cling film, bottles for squash, mineral water and shampoo 4LDPELow-density polyethyleneCarrier bags and bin liners 5PPPolypropyleneMargarine tubs, microwavable meal trays 6PSPolystyrene Yogurt pots, foam meat or fish trays, hamburger boxes, vending cups, plastic cutlery, protective packaging for electronic goods and toys 7OTHERAny other plastics that dont fall into any of the above categories E.g. melamine, which is often used in plastic plates and cups Slide 14 Table 10: Nuclear Waste TypeLow Level WasteHigh Level Waste Characteristics low activity; radioisotopes have relatively short half lives high activity; radioisotopes have long half-lives Examples items that have been used in areas where radioactive materials are handled (rubber gloves, paper towels, protective clothing, etc.) spent fuel rods from nuclear power plants DisposalStored in steel containers in concrete-lined vaults OR stored in cooling ponds until it loses much of its activity and then; filtered through ion exchange to remove Sr and Cs and then dispersed Fuel rods cased in ceramic or glass, packed in metal containers and buried deep in the earth in a location where geologists believe it wont affect groundwater Slide 15 Water and Soil Precipitation of heavy metal ions and phosphates from water When a salt is labeled insoluble, it really means that it has a very low/slight solubility in water. MX(s) M + (aq) + X - (aq) Slide 16 Water and Soil Precipitation of heavy metal ions and phosphates from water When a salt is labeled insoluble, it really means that it has a very low/slight solubility in water. Solubility product, k sp =[M + ][X - ] Slide 17 Water and Soil Many metal sulfides have very low solubility products, but can still be precipitated out by bubbling other compounds through the water, making use of the common ion effect.
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