Air-Surface Exchange of Mercury with Soils Amended with Ash Materials

Abstract

Air-surface exchange of mercury (Hg) was measured from soil low in Hg (0.013 mg/kg) amended with four different ash materials: a wood ash containing ϳ10% coal ash (0.070 mg/kg Hg), a mixture of two subbituminous coal fly ashes (0.075 mg/kg Hg), a subbituminous coal ash containing ϳ10% petroleum coke ash (1.2 mg/kg Hg), and an ash from incinerated municipal sewage sludge (4.3 mg/kg Hg) using a dynamic flux chamber. Ash was added to soil to simulate agricultural supplements, soil stabilization, and pad layers used in livestock areas. For the agricultural amendment, ϳ0.4% ash was well mixed into the soil. To make the stabilized soil that could be used for construction purposes, ϳ20% ash was mixed into soil with water. The pad layer consisted of a wetted 1-cm layer of ash material on the soil surface. Diel trends of Hg flux were observed for all of the substrates with significantly higher Hg emissions during the day and negligible flux or deposition of Hg during the night. Hg fluxes, which were measured in the summer months, were best correlated with solar radiation, temperature, and air O 3 concentrations. Mean Hg fluxes measured outdoors for unamended soils ranged from 19 to 140 ng/m 2 day, whereas those for soil amended with ash to simulate an agricultural application ranged from 7.2 to 230 ng/m 2 day. Fluxes for soil stabilized with ash ranged from 77 to 530 ng/m 2 day and for soil with pads constructed of ash ranged from Ϫ50 to 90 ng/m 2 day. Simple analytical tests (i.e., total Hg content, synthetic precipitation leaching procedure, heating, and indoor gas-exchange experiments) were performed to assess whether algorithms based on these tests could be used to predict Hg fluxes observed outdoors using the flux chamber. Based on this study, no consistent relationships could be developed. More work is needed to assess longterm and seasonal variations in Hg flux from (intact and disturbed) substrates before annual estimates of emissions can be developed.

Determination of the Potential for Release of Mercury from Combustion Product Amended Soils: Part 1—Simulations of Beneficial Use

“…The bulk soil was used to develop the materials simulating an agricultural application (Ag) and was sieved to less than 6.35 mm for use in making the stabilized soil (SS) and low-permeability surface pads (Pad). The sieving did not significantly affect the soil texture with the grain size distribution not changing significantly (79% sand, 12% silt and 8% clay 27 ). Four combustion products were amended to the soil: (1) a mixed subbituminous coal fly ash (SUB-mixed) marketed as Eagan Ash and used as a class C cement substitute; (2) wood ash (Wood) from a hybrid combined heat and power operation where 80 -90% of the heat was generated with renewable wood waste and the rest low-sulfur bituminous coal and natural gas; (3) a fly ash generated from subbituminous coal combusted with 10% petroleum coke (SUB-Pet); and (4) incinerated sewage sludge (Sludge) produced in a fluidized bed with postcombustion injection of nonimpregnated powdered activated carbon derived from coal (Donau Carbon, Deutschland; Table 2).…”

“…Materials used were originally generated for a project focused on assessment of whether algorithms could be developed between data collected from simple analytical tests (total Hg, Hg in leach solutions, Hg released when heating constantly at 80°C, and fluxes measured under controlled conditions using a small laboratory system), and fluxes measured under natural conditions could provide a simple means of predicting releases from these materials. 27 For this project, data were collected to provide a basis for consideration of the following questions:…”

“…The Ag Soil for all mixtures was a fine sandy loam with approximately 1.5% organic matter and 75% sand, 16% silt and 8% clay (cf. ref 27). The bulk soil was used to develop the materials simulating an agricultural application (Ag) and was sieved to less than 6.35 mm for use in making the stabilized soil (SS) and low-permeability surface pads (Pad).…”

“…Four combustion products were amended to the soil: (1) a mixed subbituminous coal fly ash (SUB-mixed) marketed as Eagan Ash and used as a class C cement substitute; (2) wood ash (Wood) from a hybrid combined heat and power operation where 80 -90% of the heat was generated with renewable wood waste and the rest low-sulfur bituminous coal and natural gas; (3) a fly ash generated from subbituminous coal combusted with 10% petroleum coke (SUB-Pet); and (4) incinerated sewage sludge (Sludge) produced in a fluidized bed with postcombustion injection of nonimpregnated powdered activated carbon derived from coal (Donau Carbon, Deutschland; Table 2). 27 For material generated to simulate an agricultural application (Ag), 1 part ash was homogenized into 150 parts soil on the basis of weight. For production of stabilized material (SS), 14 kg of soil was amended with 2 L of ash material and 2 L of water.…”

“…Air-surface exchange measurements made in June, July, and September 2005 were previously reported on by Ericksen and Gustin. 27 These data, along with those collected in November 2005 and February, May, and August 2006 for this project, provide a seasonal (winter, spring, summer, and fall) series of measurements.…”