RESUMEN
Airborne hexavalent chromium has been classified as a human respiratory carcinogen and long term exposure has been known to cause ulceration and perforation of the nasal septum, bronchitis, asthma, and liver and kidney damage. Chromium electroplating plants are the major sources of atmospheric chromium and packed-bed scrubbers are the common control devices used to reduce emission of chromic acid mist from electroplating bathes. The feasibility of a new method to remove this pollutant using alginate beads as a biomass derivative was investigated by one factor at a time approach and Taguchi experimental design. Polluted air with different chromium mist concentrations [10-5000 micro g/m3] was contacted to alginate beads [3.3-20 g/L], floating in distilled water with adjusted pH [3-7], using an impinger at different temperatures [20 and 35°C], and various velocities [1.2 and 2.4 m/s]. Although there were no statistical significant differences between factor levels, the higher ions removal efficiencies were achieved at lower levels of air velocities, pollution concentrations, higher levels of pHs, temperatures, and sorbent concentrations
RESUMEN
The chromium mist generator is an essential tool for research and for making evidence-based recommendations in evaluating air pollution and its control systems. The purpose of this study was to design and construct a homogeneous chromium mist generator and to look at the effects of factors such as sampling height and distance between samplers in side-by-side sampling on the chromium mist sampling method. First we developed a mist generator, using a chromium electroplating bath in pilot scale. Concentrations of CrO3 and sulfuric acid in plating solution were 125 g L-1 and 1.25 g L-1, respectively. To set up permanent air sampling locations, a Plexiglas cylindrical chamber [75 cm height, 55 cm i.d] was installed as the bath overhead. Sixty holes were made on the chamber in 3 rows [20 in each row]. The distance between rows and holes was 15 and 7.5 cm, respectively. Homogeneity and the related factors were studied using a side-by-side air sampling method. Forty-eight clusters of samples were collected on polyvinyl chloride [PVC] filters contained in sampling closed-face cassettes. Cassettes were located 35, 50, and 65 cm above the solution surface with < 7.5 and/or 7.5-15 cm distance between heads. All samples were analyzed by the NIOSH method 7600. ANOVA tests showed no significant differences between locations in side-by-side sampling [P=0.82] or between different sampling heights or sampler distances [P=0.86 and 0.86, respectively]. However, there were notable differences between means of coefficients of variation [CV] in various heights and distances. We conclude that the most chromium mist homogeneity could be obtained at a height of 50 cm from the bath solution surface and with a distance of < 7.5 cm between samplers
Asunto(s)
CromoRESUMEN
Airborne hexavalent chromium is a known human respiratory carcinogen and allergen. Many workers are exposed to hexavalent chromium in various processes which chromium electroplating plants are the most common. In this study, the feasibility of a new control approach to remove this pollutant using chitosan beads as a biosorbent was investigated. Hexavalent chromium sorption was studied relative to pH, pollution concentration, sorbent concentration, temperature, and air velocity using one factor at a time approach and Taguchi experimental design. Polluted air with different chromium mist concentrations [10-5000 micro g/m[3]] was contacted to chitosan beads [3.3-20 g/L], floating in distilled water with adjusted pH [3-7], using an impinger at different temperatures [20 and 35 °C], and various velocities [1.12 and 2.24 m/s]. The ANOVA test result showed that, there were statistical significant differences between factor levels except optimized pH levels. The higher ions removal efficiencies were achieved at lower levels of air velocities, pollution concentrations, and higher levels of solution pH values, temperatures, and sorbent concentrations