Their suitability to the site-specific conditions of a chromium electroplating plant was assessed using the results of a waste minimization audit (audit). Nicola Brown, a waste minimization expert, for her encouragement, ideas and input into my literature review in Chapter 2.
INTRODUCTION TO THE ELECTROPLATING PROCESS
BREAKDOWN OF THE ELECTROPLATING PROCESS
Immersion rinsing leaves a thin liquid film on the surface of the item that has the same concentration as the rinse tank solution. The flushing water usually enters from the bottom of the tank and leaves from the top of the opposite side.
CHEMICALS USED IN THE PRE-TREATMENT STAGE
- SOLVENT CLEANING
- SOAK ALKALINE CLEANING
- ELECTROLYTIC CLEANING
- ACID CLEANING
- NON-CHEMICAL CLEANING
These remain at the bottom of the tank when the liquid solvent evaporates again. During the process, hydrogen ions are discharged to produce hydrogen gas on the surface of the workpiece.
THE ELECTROPLATING STAGE
- THE ELECTROCHEMISTRY BEHIND ELECTROPLATING PROCESSES The voltage or potential for a reduction reaction (for example, Equation 1.11 below) under
- THE CHEMISTRY AT THE ANODE
- THE PLATING SOLUTION
- INORGANIC COMPOUNDS IN THE ELECTROPLATING SOLUTION
- ORGANIC COMPOUNDS IN THE ELECTROPLATING SOLUTION
If all the current passing through the plating bath is not used to deposit the metal plate, the cathode efficiency is said to be low. The chemistry of the electroplating solution and the chemicals used in the electroplating solution are discussed in this section.
- CHROMIUM ELECTROPLATING
Cathodic reactions are those reactions that take place on the surface of the workpieces that are covered. This means that the reduction of Cr(VI) as a dissolved species in the electrolyte, as shown in Equation 1.21, is not a true reflection of the electrochemical reduction reaction.
THE ELECTROPLATING INDUSTRY
WASTE MINIMISATION AND WASTE MANAGEMENT
Waste management looks at the use of waste minimization approaches at the top end of the hierarchy to deal with industrial waste. The hierarchy also defines the order of preference for ranking potential waste minimization efforts that can be implemented in an industrial process.
WASTE AUDITING IN THE WASTE MINIMISATION PROGRAMME
The final phase in the waste minimization program is the implementation of the most feasible of the selected waste minimization options. The waste minimization procedure can be further iterated by introducing new options to further improve the process."2. This data can then be analyzed using established waste minimization audit techniques to determine the composition, quantity and cost of the waste streams.
The range (min) is the minimum savings that can be achieved and the range (max) is the maximum savings that can be achieved by reducing waste. The waste reduction opportunities created in Stage 3 of the Waste Reduction Program (see Figure 2.3) can be applied to any of the stages in the process.
WASTE MINIMISATION OPPORTUNITIES IN ELECTROPLATING
WASTE MINIMISATION OPTIONS AND MEASURES
- DRAINAGE OF WORKPIECES
- RINSING OF WORKPIECES
- MAINTENANCE OF PROCESS SOLUTION
This is because leaching from the electroplating solution is washed off the surface of the workpiece and accumulates in this tank. This is done to limit the direct draw of rinse water into the coating bath. This water washes the process solution covering the surface of the workpiece back into the electroplating solution.
CD = Concentration of the extract entering the tank (entrainment) CR = Concentration of the rinse solution in the tank. The size of filtration systems is based on fixed load and flow rate of the plating solution.128.
COMPANY AND PROCESS PROFILE
- COMPANY DESCRIPTION
- THE CHROMIUM PLATING LINES
- THE MANUAL DECORATIVE CHROMIUM PLATING LINE
- SURFACE TREATMENT ON THE MDCPL
- RINSING ON THE MDCPL
- NON-CHROMIUM PLATING IN THE CHROME SHOP
- WASTE MINIMISATION OPTIONS USED IN AND WASTE MINIMISATION OPPORTUNITIES FOUND FOR THE MDCPL
A small rotating propeller, mounted on the side of the tank, is used to mix the cleaning solution. Every day, 70 L of the draft solutions are used to fill up the process tank. In the chromium plating bath, the ratio between the chromic acid and the sulfuric acid is kept at a fixed ratio, preferably 100:1.
Workpieces are cleaned in the alkaline weekly cleaners of MDCPL and in the pre-treatment tanks of the copper plating line before copper plating. In each week, 10 L of the draw-out is used to replenish the copper plate solution.
SCOPE AND AIMS
The six main objectives of the waste audit performed on one of these processes, the Manual Decorative Chrome Plating Line (MDCPL), are listed below:-.
MONITORING METHODOLOGY
COLLECTION OF EXISTING DATA
The table below shows the documents from which existing data has been collected from the factory for waste minimization and waste audit purposes. Material safety data sheet, technical data sheet, certificate of analysis, water accounting, water meter reading for the chrome shop, price of purchased chemicals, chrome and nickel production schedule, stock history (stock journal and supplier invoice). The chrome and nickel production chart (a chart showing the number of items plated each day in the Chrome Shop) was collected over a two-week period between 06/09/03 and 06/20/03.
This time period was used due to the large number (79911) of workpieces coated during this particular period (see Table 6.4 in Chapter 6). The inventory history and storage claims were collected over a long period of time (March to October 2003) because some chemicals are added to the application bath only at longer time intervals, which can become shorter if the output rate is increased (see Table 3.1 in Chapter 3). ).
COLLECTION OF NEW DATA ON-SITE
- RINSE WATER FLOW RATE
It was assumed that the average of the three measuring days was the flow rate of the tap water in the rinse tanks of the electroplating line. Conductivity, total dissolved solids (TDS) and pH measurements were made on site for the drag and rinse tank solutions using portable instruments (Hanna HI98311 conductivity and total dissolved solids meter {EC/TDS}, Hanna Dist WP2 total dissolved solids solids {TDS} meter and HI 98128 pH meter). Conductivity is useful for estimating the total dissolved solids content in a water sample and thus for estimating the volumetric flow rate to be used to achieve a given flushing criterion.
In general, the total dissolved solids concentration is the sum of the cations and anions and molecular species in water, usually expressed in milligrams per liter or grams per liter. pH is one of the most important measurements commonly performed in natural waters and wastewaters.
NEW DATA COLLECTED BY SAMPLING AND CHEMICAL ANALYSIS
- SAMPLING STRATEGY FOR THE MDCPL
- STORAGE OF SAMPLES
- CHEMICAL ANALYSIS OF SAMPLES
- DETERMINATION OF Cr(VI) CONCENTRATION BY UV-VISIBLE SPECTROPHOTOMETRY
- EXPERIMENTAL PROCEDURE
- DETERMINATION OF METAL CONCENTRATION BY ICP-OES
- EXPERIMENTAL PROCEDURE
The solution was clear with a lot of small items lying on the bottom of the tank. The solution was clear with a lot of items lying on the bottom of the tank. Analysis of the samples was performed after calibration of the instrument with working (calibrating) standard solutions.
The concentration of each of the metal ions in the samples collected on the two days of sampling was determined using ICP-OES. The dashes (-) indicate that no further dilution was performed to determine the concentration of the metal ions in the samples.
RESULTS
RESULTS FROM EXISTING DATA
Unit kg kg kg kg kg kg L kg kg kg package package kg kg kg L kg kg kf. Cost of the amount of rinse water used by Chrome Shop (R) Water fixed charge assigned to Chrome Shop (R). Wastewater Trade Monitoring Fee Assigned to Chrome Shop (R) Total Water Costs for Chrome Shop (R).
The trade effluent charge is calculated on the basis of a volume equal to 96% of the volume of water used in the factory. Company records were used to estimate the volume of water used by the Automatic Plating Line.
RESULTS FROM ON-SITE COLLECTION OF NEW DATA
RESULTS FROM CHEMICAL ANALYSES
- CONCENTRATION OF Cr(VI) IN THE SAMPLES
- CONCENTRATION OF METAL IONS IN THE SAMPLES
The dilution factors used for these samples are given in the experimental procedure in section 5.2.3.1. The actual (tank solution) concentrations are shown in parentheses after the measured average concentration of the analytical sample in the fifth column of Tables 6.7 and 6.8. The concentration of Cr(VI) in these original samples, before dilution, is calculated using equation 6.1.
Cr(VI) concentration = Cr(VI) concentration after dilution x Dilution factor Equation 6.1 Table 6.7 Average Cr(VI) concentration for diluted samples collected on 9/06/03. The Cr(VI) concentration shown in these tables is obtained from the results of UV-visible analysis of the samples.
DISCUSSION
DISCUSSION
- WATER USAGE
- WATER USED IN THE FLOWING RINSE TANKS
- WATER USED IN STATIC RINSE TANKS
- WATER USED IN THE DRAG-OUT TANKS
- WATER USE AS SOLVENT IN THE PROCESS SOLUTIONS
- TOTAL WATER USAGE
- REDUCING WATER USAGE
- CHARACTERISATION OF RINSE WATER SOLUTIONS
- SOAK (ACID AND ALKALINE) CLEANER'S RINSE
- ELECTROLYTIC CLEANER'S RINSE
- ACID DIP RINSE SYSTEM
- NICKEL PLATING RINSE SYSTEM
- CHROMIUM PLATING RINSE SYSTEMS
- THE COMPOSITION OF THE MDCPL RINSE SYSTEMS
- SCOPING AUDIT
- MASS BALANCE ANALYSIS
- TRUE COST OF WASTE ANALYSIS
Based on the results of the analyzes obtained from the experiments (see Appendix D), the drag of the second nickel coating (Tank 10*) is considered to be the same as for Tank 10. These values exceed (by a factor of about 2.6) the highest literature value of the range for dilution factor required for post-application washes (see Table 7.8). Accumulation of these metals in this tank can increase the concentration of metals in the tank.
In a Scoping Audit (see section 7.3.1), the source and drain of the waste need not be established as long as the level of input to and/or output leaving the process is known. Extent (max) = Maximum margin to save % x Cost/year Equation 7.9 The priority of these resources or waste streams as a waste minimization option is assigned based on one of these two costs.
CONCLUSION AND RECOMMENDATIONS
RECOMMENDATIONS
Chrome Shop water supply valve should be closed especially during tea time, lunch and hour between two shifts either manually or by installing activity based control devices. Based on the estimated water savings for just two of the flushing systems, a minimum of 4156 m3 (Rl 9949) can be achieved. The layout of the MDCPL prevents the use of drain boards between tanks which are separated by corridors.
Extending the drain time of solutions by placing drain rods above process solutions and rinse solutions on which to hang templates. Redesigning the structure of flush tanks to force water entering the top of the flush tank to leave the bottom of the opposite side (rather than the top) of that tank, or vice versa.
PRC Environmental Management, Hazardous Waste Reduction in the Metal Finish Industry, Noyes Data Corporation, Park ridge, 1989. Environmental Technology Best Practices Program, Use of Acids in the Metal Finishing Industry, EG44 Guide, Crown Copyright, Kingdom of United, Bestmentviron, 19. Program of Practice, Minimizing Chemical and Water Use in the Metal Finishing Industry, Guideline GG160, Crown Copyright, United Kingdom, March 1999.
Best Practice Program for Environmental Technology, Paint and Powder Coating Use in the Metal Finishing Industry, EG72 Guide, Crown Copyright, United Kingdom, 1996. Best Practice Program for Environmental Technology, Water Use in the Metal Finishing Industry, EG45 Guide, Crown Copyright, United Kingdom, March 1997.
