electroplating

INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

CASE STUDY #33 1. Headline: Biological degreasing with closed-rinse system 2. Background: For the Swedish electroplating company Landskrona Galvanoverk, the most important pretreatment processes are electrolytic degreasing, water-based hot degreasing, pickling and decapetion. A study showed that these processes gave rise to large amounts of waste. Environmental efforts were directed towards degreasing and pretreatment processes, with the aim of reducing pollution of the rinsing water. The conventional alkalic degreasing bath contained NaOH, soda, phosphates, silicates, tensides, and complexing and sequestering devices. The degreasing took place at pH 11-14, with a 5 per cent NaOH solution. Waste rinsing water led to an internal wastewater treatment plant where iron, zinc and chrome ions were precipitated as metal hydroxide. The resulting hydroxide sludge was dewatered in a chamber filter press. Water pollution consisted mainly of metal ions, fats, oil and tensides. Three per cent of the zinc and 15 per cent of the chrome used for finishing ended up in the rinsing water, leaving the plant partly as a component in the hydroxide sludge, which amounted to 30 tons a year; and partly as water pollution. Landskrona Galvanoverk is a small electroplating company specializing in electro deposition by zinc and chrome on steel. The turnover was US $512 000 in 1993, and seven people were employed. The company is an individual surface treatment shop with two production lines: one drum line and one conveyer line, with joint capacity of 5 500 tons a year. Both lines are equipped with the new closed system for rinsing water, biological alkalic degreasing and activated pickling. 3. Cleaner Production Principle: New technology 4. Description of Cleaner Production Application: Biological degreasing in combination with a closed-rinse water system was developed by Camex Engineering AB of Sweden. Recently, Ikaab took over the licenses. The system, based on biodegradable tensides and micro-organisms, is economical and non-polluting, with a low consumption of energy and chemicals. In general, it consists of the following steps: - objects are washed in an aqueous solution often sides - contaminants are dissolved in the washing liquid - the washing liquid is separated from the metal objects - nutrient salts are added to activate micro- organisms - natural hydrocarbons are then degraded by the micro-organisms - the tenside washing liquid can be reused All water-soluble tensides - preferably biodegradable - can be used. The pH value is kept between 8.5 and 9.4, with a temperature of 20-80 C, preferably 30-40 C, and the oil content between 50-500 mg/liter. Enabling technology: Cleansing and biodegradable can take place in one or separate baths. To activate the enzymes, BioCam 104 - a solvent free, alkaline degreasing agent with only a few additives in an environmentally benign combination - is added. The oil-eating bacteria are fed by nutrients, and become activated in the degreasing bath. The oil in which the tensides have been emulsified acts as a source for the nutrients. A separator keeps the amount of bacteria in the degreasing bath constant. The pretreatment system also includes pickling with sulfuric acid or hydrochloric acid. This method - activated oxide scale dissolving - is patented. The goods are not rinsed, as the film of biological degreasing blocks the dissolving of iron in the pickling bath. Pickling should dissolve the oxide scale (iron oxide), while keeping iron losses to a minimum. A stable precipitation of all the metals from the rinsed water is given by calcium hydroxide. The precipitate is then separated by a rotating lamella separator, and the water is returned for use during rinsing. The ion exchange equipment removes chloride ions, causing deposition of calcium sulphate (gypsum). 5. Economics: Capital investment US $421 700 Savings US $80 300 Payback period 5.5 years Savings US $ [1990] Water 10 8000 Energy 7 1000 Chemicals: - Inhibitor (pickling bath) 10 000 - Degreasing substance 7 800 - Sulfuric acid 6 700 24 600 Service, shutdowns: - Sulphate handling 32 400 - Degreasing bath 5 400 37 800 6. Advantages: Before After Waste generation 30 t 10 t hydroxide sludge Feedstock use 20% 8% sulfuric acid Water use 8 000 800 m3/year 7. Constraints: N/A 8. Contacts:Landskrona Galvanoverk Gasverksgatan 23 S-261 35 Landskrona Sweden Tel: +46 418 411936 Lars Siljebratt TEM, University of Lund Asumgatan 38 S-27537 Sj"bo Sweden Tel: +46 416 27 3000 Fax: +46 416 27 312 Annelies den Braber TME, Institute for Applied Environmental Economics Grote Markstraat 24 2511 BJ The Hague Netherlands Tel: +31 70 3464422 Fax: +31 70 36 23 469 9. Keywords:Sweden, Netherlands, Landskrona, metal, electroplating, new technology, biotechnology, enzyme, ion exchange, degreasing, zinc, chrome 10. Reviewer comments: This case study was originally published in the UNEP IE document "Cleaner Production Worldwide", Volume II. In the process of preparing the document the case study underwent a technical review.