Waste Minimization of Hazardous Waste Solutions in the Electroplating and Precious Metals Industry Using the Final Treatment Distillation Unit

Transcription

1 Waste Minimization of Hazardous Waste Solutions in the Electroplating and Precious Metals Industry Using the Final Treatment Distillation Unit Paul Wavrock Drew Resource Corporation The disposal of hazardous waste solutions, such as cyanide solutions, used in the electroplating industry has always been a technical and economic problem. Regulations continue to become more stringent as to where and how long this waste is stored, as well as the methods of storage and disposal. Disposal costs continue to increase. Is there a solution to this problem? The FINAL TREATMENT Mstillation Unit uses a new method to concentrate the cyanide ions in order to minimize the volume of the waste solution. Two options exist with the concentrated solutions: 1) "he solutions may be concentrated to a sludge to minimize the volume of hazardous waste. This can then be sent for metal recovery. 2) Drag-out solution or static wash m y be reduced to about 25% of the volume. A chemical adjustment can be done to match the plating solution, then, use this solution to "top up" the plating tank. In this manner there is no sludge to dispose of as a hazardous waste. The concentration operation, although simple in theory, has always been subject to severe practical limitations related to costs. The separation of water from any kind of salt, in fact, consumes a great deal of energy. Our Prs Distillation Unit includes three major features designed to reduce the energy requirements of this process to just 0.2 KW per litre of solution treated: 1) As the unit operates in a residual vacuum of d g, the distillation process is carried out at a temperature of only 30-3S0 c- Thus, energy costs are 80% less than at standard atmospheric pressure. 2) The energy required to boil the liquid is supplied by a freon-type heat pump. This unit provides the heat required for evaporation and the refrigeration for condensation. 109

2 3) The surface on which the heat exchange takes place is constantly cleaned by a rotating blade. The problems of residue and the effects on thermal efficiency are therefore solved. The operation of the unit is illustrated in fig. 1. R IO BOILING CHAMBER EXPANSION VALVE AIR HEAT EXCHANGER INLET FOR SOLUTION TO BE EVAPORATED HEATING JACKET CONDENSATION CHAMBER DISTILLATE TANK BOTTOM SCRAPING SYSTEM DISCHARGE OF CONCENTRATED PRODUCT REFRIGERANT COMPRESSOR OUTLET FOR DISTILLED LIQUID EJECTOR EJECTOR PUMP Please Note: That the Final Treatment System is a distillation - not evaporation system. No potentially harmful vapors are released to the air. Instead vapors are condensed and are captured as a distilled water. If the distillate still does not meet the sewer discharge guidelines, it can be further treated with a resin system, such as the Drew AQUA CLEAR Systems A detailed technical description is available on request. However, we feel that some of the advantages found in certain applications of low-temperature vacuum distillation should be underlined. The tests described below were carried out by: GALVA" anc JULLWRK REFINING COW. Via A. Volta, 7 and 1743 Cedardale Road TORR1 DI QUSRTESOLO (VI) Mount Vernon, Washington Italy The results of the analysis were obtained using an PERKIN ELMER 303 atomic 110

3 absorption spectrophotometer for metals with volumetric measurements and using N/10 silver nitrate titration for the cyanide ions. ELAMPLE1 Nickel drag-out A) Composition of nickel-plating solution: Nickel chloride: 80 g/1 approx. Nickel sulphate: 280 g/1 approx. Boric acid: 40 g/1 approx. pa: 4.5 Density: B B) Composition of nickel drag-out solution (4 static stages): Nickel chloride: 10 g/l Nickel sulphate: 25 g/1 Boric acid: not measured pa: 6.5 Density: 10 B C) Composition of distillate: Nickel : <0.05 mg/l Sulphate : <1.00 mg/l Chloride : (1.00 mg/l pa: 8.1 Volume of distillate: 85% Volume of concentrate: 15% Silver drag-out mixed with silver plating solution A) Composition of silver plating solution: Silver 40 g/1 approx. Cyanide 120 g/1 approx. pa: 12.5 Carbonate 40 g/l Surface active agents 45 g/1 B) Composition of solution to be distilled (silver plating solution and silver drag-out for silver recovery): Silver 10 g/1 Cyanide 40 g/1 Carbonate 10 g/1 Surface active agents not measured Pa 11 C) Composition of distillate: Silver <0.2 mg/l Cyanide 72.5 mg/l pa: 8.9 Volume obtained: 80% Volume of concentrate: 20% 111

4 Gold dranout from gold-removal solution A) Composition of solution to be distilled: Gold 3.2 g/1 Cyanide 8.2 g/1 PH: 8.2 Copper 1.3 g/1 Silver 0.32 g/1 Nickel 0.15 g/1 Surface active agents 4 g/1 B) Composition of distillate: Gold < 0.05 mg/l Cyanide 28 mg/l Copper 0.05 mg/l Silver < 0.05 mg/l Nickel 0.05 mg/l Volume obtained: 85% Volume of concentrate: 15% passivation drag-out solution A) Composition of solution to be distilled chromium 6k 2.1 g/1 Surface active agents 1.1 g/1 B) Composition of distillate EXAMPLE5 chrolaium qgl Surface active agents traces Volume obtained: 95% Volume of concentrate: 5% Solution for ultrasonic degreasing equipment A) Composition of solution to be distilled PH 12 Copper Surface active agents 12 mg/l 8 g/1 B) Composition of distillate PH 8.5 Copper <0.05 mg/l Surface active agents traces In some cases, it was not possible to sewer the distillate, whose concentration was in excess of the limits laid down by Italian legislation. In these cases, the distillate was treated using specific selective resins in order to remove the metallic cyanide compounds. 112

5 The values measured at the output of the resin exchangers are given below. Cyanide < 0.05 mg/l The resins can absorb approximately g of gold cyanide for each liter of resin per regeneration cycle. It should be underlined that the FTS Distillation unit does not destroy the cyanide ions, but reduces their volume as far as possible. This gives the following advantages: Reduced volume of the material sent for metal recovery Reduced disposal costs Reduced storage area for hazardous waste. Increased control of the recovery process Examples of Cost Savings with FINAL TREATMENT SYSTEMS A plating shop generating an average of 40 gallons of nickel drag-out solutions per day. They pay $5,00/Gal, for a licensed waste hauler to pick up 3600 gal./w days for removal to a state approved disposal site. A FINAL llwlment 50 is purchased for $14,800.00, which will result in a waste reduction of 85% by volume (540 gallons/90 day period). Pre FTS 50 Disposal: with FTS 50 - Disposal: 6 Gal./Day X $5.00/Gal. - $30.00/hy Treatment Charge - Assume 9t!/KWB 40 Gal./Day X $OOO68/Gal =$ 2.72/Da~ $32.72/Day Daily Savings $ Payback Period $ = 88.5 Days $ /Day Therefore, the unit pays for itself in less than three months. Circuit Board Manufacturer "B" produces 125 gallons/day of waste cyanide solutions. Every 90 days they pay a licensed transportation and disposal company $4.75/Gal0 to remove 11,250 gallons of cyanide waste. The manufacturer is contemplating purchasing a FINAL TREARIENT 150 for $46,500 and an AQUA CLEAR 30 for $18,300 to further treat the distillate. 113

6 Present Method : 125 Gal./Day X $4.75/Gal. = $ with PTS 150: Gal/Day X $4.75/Gal. = $ Operating Cost 125 Gallons X $0.068/Ga1. - $ Gallons X $0.0038/Gal. = $ 0.40 $ Daily Savings $ Payback Period $64,800 = Days $495.79/Day For a full system, the payback period is less than 4.4 months. Additional Benefits to Owning a...final TRWM3NT SYSTEEI... 1) Reducing the volume of hazardous waste stored can result in reducing the size (or avoiding an expansion) of the hazardous waste storage area, and a saving in the costs associated with maintaining this area. (e.g. lower insurance rates) 2) In the event of a leak, a sludge leak is easier to contain than a liquid leak. 3) In filling out biannual reports of hazardous waste manifests, companies are requested to present their plans for hazardous waste reduction. The FINAL TREA"T SYSTEM allows WASTE REDUCI'IONS of 8045% SUMMARY The FINAL TREA"T vacuum distillation system allows metal platers to meet their waste minimization goals and save money at the same time. This equipment reduces the volume of hazardous waste by removing the non-hazardous solvent (e.g. water) leaving the concentrated chemicals behind. If drag-out solutions are concentrated to be used to "top-up" the plating solution, there is no hazardous waste left behind. By reducing the hazardous waste volume and thereby reducing the disposal cost, the equipment pays for itself rapidly. Metal recovery is, in fact, easier from the concentrated sludge. Since there are no harmful vapors giveo off to the atmosphere, the FINAL TBEAm SYSTEM becomes 9~? ideal component of a pollution abatement system. 114