Particle size distribution and dissolution properties of metals in cyclone fly ash

Abstract

ABSTRACT:The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution.

Cyclone fly ash from a grate-fired biomass combustion plant: Dependence of the concentration of various components on the particle size

“…But also for Ba and V in the finest particle class an enrichment of comparable range was reported which is in contrast to the depletion of these components in the finer particle classes found in this study. For Pb no dependence of the concentration on the particle size was found in [18] whereas in this study the enrichment of Pb in the finer particle classes was very similar to those of Zn and Cd.…”

“…For the coarse size range with the coarsest particle class of 250-500 μm and the finest particle class (b75 μm) a similar ratio of the concentrations of Cd and Zn in the finest particle class to the concentration in the coarsest particle class was found [18]. But also for Ba and V in the finest particle class an enrichment of comparable range was reported which is in contrast to the depletion of these components in the finer particle classes found in this study.…”

“…But there is not very much information available on the dependence of the composition of the fly ash on the particle size. The distribution of heavy metals in the four size fractions of a cyclone fly ash originating from a grate-fired boiler combusting forest residue was investigated in one study [18]. In this study a vibrating sieve shaker was used to split the fly ash into the particle classes 250-500 μm, 125-250 μm, 75-125 μm and b75 μm.…”

Evaluation of sediment contamination with heavy metals: the importance of determining appropriate background content and suitable element for normalization

“…One Teflon vessel only contains the acid mixture for a blank. A microwave digestion system brings the sample to 165°C in 10 min (holding time 0 s), then 175°C in 3 min, where held for 10 min (max power was 1200 W) (Rönkkömäki et al 2008). Microwave digestion was performed in a pressurized microwave oven (Ethos 1, Advanced Microwave Digestion System, Milestone, Italy) equipped with a rotor holding 10 microwave vessels (PTFE).…”

Preliminary Study of Trace Metals by Environmental Quality Criteria in Sediments from a Mangrove Forest inSaco do Mamanguá(Ilha Grande Bay, Rio de Janeiro, Brazil)

“…This protocol is recommended for the United States Environmental Protection Agency (USEPA) to leach metals and has been widely applied in sediment, soil and sludge samples. 29,30 0.50 g of sediment sample was weighed carefully into a Teflon digestion tube and 10 cm 3 of concentrated HNO 3 was added. Then the tubes were closed and the samples were heated in the microwave oven (Anton Paar -Multiwave 3000) under the following conditions: pressure 20 bar, power 1200 W; heating program: in the first step, the temperature was increased linearly from 25 to 175 °C in 5.3 h and in the second step, the temperature was held at 175°C for 4.3 h. Blank solutions and certified reference material NIST-8704 (Buffalo River Sediment) were prepared in the same way.…”