W. P. Miller

A micro‐pipette method for soil mechanical analysis

Abstract Determination of soil texture, particularly the clay (<2 μm) fraction, is an important measurement in most soil investigations. In this study a modified method for mechanical analysis was evaluated that eliminated the need for bulky laboratory equipment and long settling times associated with standard pipette and hydrometer methods. Termed a “micro‐pipette”; method, the modified procedure uses 2 to 4 g soil with 40 mL of dilute dispersant, shaken overnight in 50 mL centrifuge tubes. Clay is determined by sampling 2.5 mL using an adjustable volume pipettor from a depth of 2.5 cm after approximately 2 h of settling, as calculated from Stokes’ law. The dried suspension weight is used to compute clay content after correction for salt content of the dispersant. Sand can be determined by sieving at 50 μm after clay analysis, with silt calculated by difference. Using 12 soils with a range of particle sizes, the proposed method was found to give textural values nearly identical to those found with the st...

Composition and element solubility of magnetic and non-magnetic fly ash fractions.

Magnetic and non-magnetic fractions of coal fly ashes from SE US electric power plants were characterized with special emphasis on the potential environmental consequences of their terrestrial disposal. Quartz and mullite were the crystalline minerals dominating the non-magnetic fractions. Magnetic fractions contained magnetite, hematite, and, to a lesser extent, quartz and mullite. Chemical analyses revealed that magnetic fractions had about 10 times higher concentrations of Fe, and 2-4 times higher concentrations of Co, Ni, and Mn. Non-magnetic fractions were enriched in K, Al and Ca. Iron content within fly ash particles was negatively correlated with elements associated with aluminosilicate matrix (Si, Al, K, Na). Solubility of most elements was higher in the non-magnetic than in the magnetic fractions of alkaline fly ashes at comparable pH. Calcium was associated with the non-magnetic fraction of the alkaline fly ashes which resulted in a higher pH buffering capacity of this fraction.

Permissible Concentrations of Arsenic and Lead in Soils Based on Risk Assessment

Establishing permissible concentrations for As and Pb in soils is of practical importance because of toxicity of these metals, their widespread contamination, and limited resources available for remediation of contaminated soils. The USEPA pathway approach to risk assessment was used to assess an environmental hazard related to As and Pb in soils and to evaluate safe concentrations of these metals in contaminated soil. The results from large-scale field experiments with soil fly ash-biosolids blends were used as input data to analyze pathways of the most intense transfer of the contaminants to a target organism. A direct soil ingestion by children (the soil-human pathway) was considered the most important exposure route to soil As and Pb. A conservative risk analysis shows that As concentrations in soil can reach 40 μg g-1 without a hazard to exposed organisms. A Pb concentration in soil up to 300 μg g-1 does not cause an excessive intake of Pb by humans as evaluated by a direct soil ingestion exposure model.

Arsenic and selenium speciation in coal fly ash extracts by ion chromatography-inductively coupled plasma mass spectrometry

Ion chromatography (IC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) affords a sensitive technique to quantify inorganic As and Se species at trace levels; however, few studies have used the multi-element capabilities of ICP-MS as a detector for chromatographic applications. Here, IC coupled with ICP-MS was used to determine As(iii), As(v), Se(iv), and Se(vi) in aqueous extracts of coal fly ash. All four species were resolved, with retention times of 1.1, 2.9, 4.8, and 6.3 min for As(iii), Se(iv), Se(vi), and As(v), respectively. Because all species were fully resolved, the resulting chromatograms were obtained by summing signal intensities form/z 75+m/z82. Absolute detection limits of 7.2, 87, 117, and 28 pg for As(iii), Se(iv), Se(vi), and As(v), respectively, were obtained, corresponding to 0.072, 0.868, 1.174, and 0.284 µg l–1 for a 100 µl injection volume. The technique was used to determine the speciation of As and Se in aqueous extracts of 24 coal fly ash samples including NIST SRM 1633b. The predominant species were As(v) and Se(iv), with As(iii) detected in two low pH fly ashes. Extraction of fly ashes at pH 5 altered the concentrations of total soluble As and Se but did not affect the predominant As and Se speciation.

Dissolution of synthetic crystalline and noncrystalline iron oxides by organic acids

Abstract Thirteen organic acids and fulvic acid were used in dissolution experiments with laboratory-synthesized noncrystalline Fe oxide, hematite and goethite to determine the effect of the organic acid properties on the kinetics and pH-dependence of oxide dissolution. After 100 h of reaction the noncrystalline oxide had completely dissolved at pH 3.5 in the presence of oxalic, malonic, malic, citric and tartaric acids as well as EDTA, DTPA and NTA. Acetic, lactic, salicylic, phthalic and fulvic acids were much less reactive. Dissolution was generally lower at pH 5.5 than at pH 3.5. Hematite and goethite were solubilized to a much lesser extent than the noncrystalline oxides, presumably due to lower surface areas and differences in type and arrangement of surface hydroxyl and oxygen groups. Oxide solubilities predicted using formation constants of Fe-organic acid complexes approximately predicted dissolution measured at 100 h for the different acids used with the noncrystalline material, whereas slow reaction times limited dissolution of hematite and goethite to levels far below those predicted. The differences observed in pH-dependence and kinetics were explained on the basis of adsorption onto variable-charge surfaces and as steric limitations for the large chelating acids.

Arsenate Displacement from Fly Ash in Amended Soils

Arsenic (As) is the biggest environment contaminant in most of the soils where fly ash is applied. Usually, it is not mobile and strongly adsorbed on to soil particles. However, in gypsum and phosphorus amended soils As may be much more mobile. A study in repacked columns was conducted to determine whether or not As becomes mobile when Ca(H2PO4)2and CaSO4are used as leaching solutions, and to compare the competitive interactions between PO4-AsO4and SO4-AsO4. Arsenic concentration in leachate was found to be approximately ten times greater when Ca(H2PO4)2was used to leach the columns as compared to CaSO4. A maximum concentration of 800 μg As L-1was found in the leachate in this case, which is much higher than the groundwater limit of 50 μg L-1for drinking water established by the United States Environmental Protection Agency. In fly ash, the portion of arsenate non-specifically adsorbed is believed to be much lower than that of specifically adsorbed. Sulfate anions were able to displace only non-specifically adsorbed arsenate. In this case the concentration of As in leachate was found to be within acceptable limits. On the other hand, phosphate can compete with arsenate for all available adsorption sites, non-specific and specific. Phosphate displacement of both forms of arsenates increases As mobility in both control and fly ash treatments.

Ionic tracer movement through highly weathered sediments

A highly-weathered, sandy aquifer material from the Upper Coastal Plain region of the southeastern U.S.A. (Aiken, South Carolina) was used to determine the impact of ionic strength and solution composition on the determination of physical transport parameters using ionic tracers. The mineralogy of the clay fraction consisted primarily of kaolinite, goethite and mica. Repacked saturated columns (bulk density ∼ 1.5 g cm−3) were leached at a constant rate (∼ 0.25 cm min−1) with a given tracer solution. For comparison, tritium (∼ 200 pCi mL−1) was included in leachate of selected columns and several of the experiments were replicated in columns of acid-washed sand. Pore volume estimates based on tritium breakthrough were consistent with those calculated from the bulk density of the repacked matrix. In contrast, solute breakthrough for the sandy geologic material was dependent on concentration, as well as cation and anion type. At low ionic strenghts (0.0005–0.010 M) that are analogous to conditions that may be encountered ins field-scale transport experiments, neither the cation nor the anion acted conservatively, yielding systematically high estimates of column porosity or low estimates of flow velocity. At the higher ionic strengths (∼ 0.10 M), solute breakthrough was essentially conservative regardless of ionic composition. The impact of cation valence and concentration on Br− breakthrough was determined using MgBr2 and KBr solutions of varying concentrations (0.001–0.1 N). Bromide breakthrough was substantially delayed for concentrations below 0.10 M and was delayed to a greater extent in the presence of a divalent cation (Mg2+) than in the presence of a monovalent cation (K+). Failure to recognize these interactions in the field could lead to a false interpretation of Br displacement in terms of physical interactions, i.e. flow velocity, dispersivity, etc.

Release of Nitrogen and Phosphorus from Poultry Litter Amended with Acidified Biochar

Application of poultry litter (PL) to soil may lead to nitrogen (N) losses through ammonia (NH3) volatilization and to potential contamination of surface runoff with PL-derived phosphorus (P). Amending litter with acidified biochar may minimize these problems by decreasing litter pH and by retaining litter-derived P, respectively. This study evaluated the effect of acidified biochars from pine chips (PC) and peanut hulls (PH) on NH3 losses and inorganic N and P released from surface-applied or incorporated PL. Poultry litter with or without acidified biochars was surface-applied or incorporated into the soil and incubated for 21 d. Volatilized NH3 was determined by trapping it in acid. Inorganic N and P were determined by leaching the soil with 0.01 M of CaCl2 during the study and by extracting it with 1 M KCl after incubation. Acidified biochars reduced NH3 losses by 58 to 63% with surface-applied PL, and by 56 to 60% with incorporated PL. Except for PH biochar, which caused a small increase in leached NH4 +-N with incorporated PL, acidified biochars had no effect on leached or KCl-extractable inorganic N and P from surface-applied or incorporated PL. These results suggest that acidified biochars may decrease NH3 losses from PL but may not reduce the potential for P loss in surface runoff from soils receiving PL.

A micro‐pipette method for water dispersible clay

Abstract The clay percentage determined by mechanical means in distilled water without the removal of organic matter and soluble salts and use of a chemical dispersant, is referred to as water dispersible clay (WDC). In this study, a “micro‐pipette” WDC method is developed and described. The method increases laboratory production, i.e., number of samples per day, and yet requires less laboratory space and time. In addition, this method yields, for most soils, WDC values comparable to those values obtained by the standard SCS “macro‐pipette” method. Statistical analysis of variance (ANOVA) for determination of WDC percent indicates nonsignificant effects at α = 0.05 for both method and method times soil but significant effects for method times soil interaction term at α=0.10. In order to characterize the particle‐size distributions, a moment analysis was run on each of the 14 soils. In this study, the distributions of most soils measured by the “macro‐pipette” method are not significantly different by the ...

EXCHANGE AND APPARENT FIXATION OF LITHIUM IN SELECTED SOILS AND CLAY MINERALS

Relatively few data exist on the exchange reactions of Li in soils; rather, the bulk of the literature has dealt with simple ion exchange reactions on ideal exchangers, usually synthetic resins or pure clay minerals. Occasional observations of anomalous exchange of Li have been reported, without any clear explanation. This study was initiated to more carefully examine Li exchange in complex soil-solution and clay mineral systems. At the low concentrations employed, Li was sorbed preferentially by the southeastern U.S. soils evaluated over excesses of Na, K, Mg, and Ca in the adsorption solution phase. Trace amounts of Li were also sorbed to bentonite, kaolinite, and vermiculite clay samples in the presence of 0.01 M Mg(NO3)2 (5.82, 3.67, and 8.37 μg g−1, respectively). The bentonite retained no Li against displacement by M NH4Cl, but both the kaolinite and vermiculite fixed a substantial portion of the total sorbed Li (57 and 60%, respectively). Similarly, at low Li additions to an Iredell surface soil sample (0 to 2.4 mmol kg−1), a significant portion of the sorbed Li was fixed against displacement by M NH4Cl, M CsCl, 0.5 M MgCl2, and 0.05 M HCl/0.012 M H2SO4 (e.g., 77.0, 79.2, 82.0, and 75.9%, respectively, at a 1.1 mmol kg−1 loading). The rate of Li sorption to the Iredell surface soil was slowed in the presence of a 0.005 M MgCl2 background relative to an absence of background electrolyte. The extent of sorption was also reduced to 80% of that observed without supporting electrolyte, in agreement with the mass of Li observed to be fixed against displacement in the desorption study. The source and nature of sorption sites within soils and clay minerals that have this high selectivity for Li remain unclear, although vacant octahedral positions at the mineral edge may be responsible.