FREEZE CONCENTRATION AND RECYCLE OF PLATING WASTES

RINSE WATER AND OTHER AQUEOUS WASTES FROM METAL FINISHING OPERATIONS PRESENT A DISPOSAL PROBLEM BECAUSE OF THEIR HEAVY METAL AND AGGRESSIVE CHEMICAL CONTENT. GENERALLY, THESE WASTES ARE TREATED CHEMICALLY TO PRECIPITATE THE METALIONS AS OXIDES OR HYDROXIDES. THIS TREATMENT IS COSTLY BECAUSE IT INVOLVES THE ADDITION OF CHEMICALS, DISPOSAL OF SLUDGE WITH LOSS OF VALUABLE METALS, AND LOSS OF THE HIGH PURITY WATER REQUIRED FOR RINSING OPERATIONS. FREEZE CONCENTRATION PROCESSES HAVE DEMONSTRATED POTENTIAL FOR RECOVERING PURE WATER FOR RECYCLE TO THE RINSING OPERATION WHILE PRODUCING A CONCENTRATED STREAM SUITABLE FOR REUSE IN PLATING BATHS. CONCENTRATION BY EVAPORATION IS COSTLY DUE TO THE CORROSIVITY OF THE SOLUTIONS AT HIGH TEMPERATURE. MEMBRANE PROCESSES MAY NOT BE APPLICABLE WHEN OXIDIZING CHEMICALS ARE PRESENT. THERE IS SIGNIFICANT DATA AVAILABLE FOR THE DESIGN OF FREEZING PROCESSES FOR THE PRODUCTION OF PURE WATER FROM SEA AND BRACKISH WATERS. THE OBJECT OF THIS INVESTIGATION IS TO OBTAIN THE DESIGN DATA NECESSARY TO OPTIMIZE FREEZE CONCENTRATION OF WASTE STREAMS FROM METAL FINISHING OPERATIONS. A BENCH SCALE PLANT WILL BE ASSEMBLED TO PROCESS SIMULATED RINSE WATER FROM CHROME, NICKEL, COPPER, AND CADMIUM PLATING OPERATIONS. OPERATING DATA WILL BE OBTAINED AS A FUNCTION OF SOLUTION CONCENTRATION. THE BENCH SCALE PLANT WILL BE OPERATED AT FREEZING TEMPERATURES DOWN TO 22 DEGREES FAHRENHEIT. BASED ON SEAWATER DATA, THIS WILL OCCUR AT A CONCENTRATION OF 10% TDS, REPRESENTING ABOUT 98% RECOVERY OF PURE WATER AND REDUCTION OF THE WASTE VOLUME TO 2% OF THE ORIGINAL WASTE STREAM. THE DATA IS EXPECTED TO VERIFY EXSTAR'S DESIGN CONCEPT FOR A LINE OF ECONOMICAL PACKAGED WASTE CONCENTRATION PLANTS RANGING IN SIZE FROM 1,000 TO 20,000 GALLONS PER DAY (GPD. IN PHASE II, A TRANSPORTABLE 5,000 GPD PLANT IS PLANNED FOR DEMONSTRATION ON ACTUAL WASTE STREAMS. EXSTAR HAS THE FACILITIES AND BUSINESS ORGANIZATION NECESSARY TO COMMERCIALIZE THE PROCESS IN PHASE III.