SIZE AND CONCENTRATION MEASUREMENTS OF PARTICLES PRODUCED IN COMMERCIAL CHROMIUM PLATING PROCESSES

Optical measurements of particle size and concentration were made at t he chromium plating tank and exhaust system at a commercial hexavalent chromium plating facility. Particles were examined at three locations in the exhaust system: 1) directly at the hexavalent chromium plating bath surface, 2) at the exit of a cyclone separator located in the ex haust system approximately three to four meters downstream of the bath , and 3) in the exhaust stack, downstream of the induced draft fan and all abatement devices. Particle diameters at the bath surface ranged from 0.3 to 25 mu m. Downstream of the cyclone exit and mesh pad filte rs, particle top sizes were approximately 5 and 0.7 mm, respectively. On a mass basis, the collection efficiency of all abatement devices wa s 99.997%. Assuming that droplets in the flow consist primarily of wat er and chromium, correcting the total particle mass flow against water content gives a chromium emission rate of 64,000 mu g/hr, which compa res favorably with a value of 77,000 mu g/hr measured with EPA methods . This initial agreement, which should be validated through additional measurements over a broad range of flow conditions, raises the possib ility of continuous monitoring for chromium metal emissions using part icle size/mass as a surrogate.