Chemical characteristics of selected flyash leachates

Abstract

The physical characteristics of selected flyashes and the quantity of leachate generated from those ashes are evaluated in order to provide the data base needed to develop an environmentally safe disposal management strategy. Ash samples from three sources (1) Clinch River Power Plant at Carbo, Virginia; (2) John Amos Power Plant at St. Albans, West Virginia; and (3) a “Standard” flyash from the National Bureau of Standards were examined. These samples were leached with water according to ASTM extraction procedures and then the leachates were analyzed to determine the total filterable residue, hardness, calcium, sulfate and phosphate concentrations, acidity/alkalinity, and pH. Trace element concentrations were determined by atomic absorption spectrophotometry.

Total filterable residue values for the five leachates studied ranged from 180 mg/1 to 1743 mg/1; hardness ranged from 176 mg/1 to 985 mg/1 (as CaCO,), with calcium concentrations ranging from 69 mg/1 to 310 mg/1; and sulfate concentrations ranged from 148 mg/1 to 916 mg/1. The NBS flyash produced the only acidic leachate and exhibited the highest concentrations of Cd, Co, Cu, Mn, Ni and Zn. All of the trace elements determined were found at concentrations of less than 1.0 mg/1.

Ash composition as a function of particle size was studied using the John Amos ash. Samples were sieved into two size fractions; one 53μ and smaller, and the other larger than 53μ. The leachate of the particles greater than 53μ in size has consistently lower values of total filterable residue, hardness, calcium and sulfates.

Key words:

• Leachate
• Flyash
• Coal Combustion
• Heavy Metals