Behaviour and dynamics of di-ammonium phosphate in bauxite processing residue sand in Western Australia—I. NH<Subscript>3</Subscript> volatilisation and residual nitrogen availability

Background, aim and scope

Australia is the largest producer of bauxite in the world, with an annual output of approximately 62 million metric dry tons in 2007. For every tonne of alumina, about 2 tonnes of highly alkaline and highly saline bauxite-processing residue are produced. In Western Australia, Alcoa World Alumina, Australia (Alcoa) produces approximately 15 MT of residue annually from its refineries (Kwinana, Pinjarra and Wagerup). The bauxite-processing residue sand (BRS) fraction represents the primary material for rehabilitating Alcoa’s residue disposal areas (RDAs). However, the inherently hostile characteristics (high alkalinity, high salinity and poor nutrient availability) of BRS pose severe limitations for establishing sustainable plant cover systems. Alcoa currently applies 2.7 t ha^?1 of di-ammonium phosphate ((NH₄)₂HPO₄; DAP)-based fertiliser as a part of rehabilitation of the outer residue sand embankments of its RDAs. Limited information on the behaviour of the dominant components of this inorganic fertiliser in highly alkaline BRS is currently available, despite the known effects of pH on ammonium (NH₄) and phosphorus (P) behaviour. The aim of this study was to quantify the effects of pH on NH₃ volatilisation and residual nitrogen (N) in BRS following DAP applications.

Methods

The sponge-trapping and KCl-extraction method was used for determining NH₃ volatilisation from surface-applied DAP in samples of BRS collected from each of Alcoa’s three Western Australia Refineries (Kwinana, Pinjarra, Wagerup) under various pH conditions (pH 4, 7, 9 and 11). Following cessation of volatilisation, the residual N was extracted from BRS using 2 M KCl and concentrations of NH ₄ ⁺ –N and NO ₃ ^? –N were determined by flow injection analysis.

Results

The quantities of NH₃ volatilised increased dramatically as the pH increased from 4 to 11. Much of the N lost as NH₃ (up to 95.2%) occurred within a short period (24 h to 7 days), particularly for the pH 9 and 11 treatments. Concentrations of residual NH ₄ ⁺ –N recovered in DAP-treated BRS at the end of the experiment decreased with increasing pH. This finding was consistent with increasing loss of N via volatilisation as pH increased. The concentration of NO ₃ ^? –N was very low due to no nitrification in BRS.

Discussion

The pH was a key driver for NH₃ volatilisation from DAP-treated BRS and primarily controlled N dynamics in BRS. Results indicate that NH₄ not adsorbed by BRS was highly susceptible to volatilisation. The likely lack of nitrifying bacteria did not allow conversion of ammonium to nitrate, thereby further exacerbating the potential for loss via volatilisation

Conclusions

It was demonstrated that the pH is the key factor controlling the loss of inorganic N from BRS. Although volatilisation was considerably lower at pH 4, achieving this pH reduction in the field is not possible at present. Findings from this study highlight the need to better understand which forms of N fertiliser are most suitable for use in highly alkaline BRS.

Recommendation and perspectives

Although pH reduction is the most likely means of stopping NH₃ volatilisation in BRS, it is economically and operationally unfeasible to add sufficient acidity for adequately lowering pH in the BRS for revegetation. More attention on forms of fertilisers more suitable to highly alkaline, microbially inert soil conditions appears to be warranted.

     

Interaction between co‐solvents and algae in the residue dynamics of fenitrothion

Abstract

Fresh and estuarine water algae maintained in laboratory microcosms simulating river‐lake/estuary‐bay systems were exposed to ¹⁴C‐fenitrothion formulated with Atlox and tank mixed with Aerotex or Dowanol (11.5:1.5:1.5 w/v/v). Generally, the tank mix co‐solvents determined the amount of uptake and the array of derivatives formed by the algae. Typically, exposed to an Aerotex mix the ratio of ethyl acetate extractable (NP) fraction : ethyl acetate unextractable (P) fraction was as 3.5:1.0, exposed to a Dowanol mix the ratio was as 1.5:1.0. Within any comparable time period, fresh water algae turned over more of the C‐ring of fenitrothion than the estuarine genera. Turn‐over was enhanced when Aerotex was the tank mix co‐solvent.     

A chamber study of photochemical smog in Melbourne,Australia—present and future

The present paper concludes a comprehensive program designed firstly to locate the source areas of emission responsible for the photochemical smog which impacts the central Melbourne urban area, secondly to determine the hydrocarbon and NO_x composition of these sources and finally to demonstrate by smog chamber simulations what benefit would be derived from a reduction in the emissions from the offending sources.The conclusions reached are that a reduction in NO_x emissions would lead to increased ozone levels in Melbourne but even a small reduction in hydrocarbon emissions would be beneficial. The implementation of Australia Design Rule 37 should, by restricting hydrocarbon emissions to 50% of the current 1985 level, reduce the photochemical ozone over the central metropolitan area to well below the acceptable level.In the course of this work it has been possible to validate the chamber technique by showing that the photochemical behaviour of a well-documented air parcel can be reproduced in a smog chamber operated under the same conditions of temperature, radiation, dilution and pollutant input as was experienced by the outdoor air parcel.     

Atmospheric equilibrium model of sulfate and nitrate aerosols—II. Particle size analysis

Part I of this work presented a thermodynamic equilibrium model for the quantity, composition, and physical state of atmospheric sulfate/nitrate/ammonium aerosols. In this work we extend that model to include particle size. That is, given total nitrate and ammonium levels, relative humidity and temperature, and the distribution of sulfate by particle size, we calculate the equilibrium quantity, composition, and physical state of the aerosol as a function of particle size. The model provides an explanation for the differences in observed ambient sulfate and nitrate size distributions.     

Evolution of particles in the plumes of coal-fired power plants—II. A numerical model and comparisons with field measurements

A three-dimensional numerical model is described which considers the effects of advection, diffusion, coagulation, gravitational settling, gas-to-particle (g-to-p) conversion and interactions with the ambient air on the evolution with time of particle size distributions in power plant plumes. From inputs of an atmospheric temperature, humidity and wind sounding, and the concentrations of particles and trace gases emitted from a power plant and in the ambient air, the model provides predictions of the particle size distributions, total particle concentrations, concentrations of trace gases, g-to-p conversion rates and the light-scattering coefficient of the particles at points in the plume downwind of the stack.Comparisons of the model predictions with airborne measurements obtained in the plumes from two coal-fired power plants show that the model is capable of predicting many of the principal features of the evolution of the particle size distributions and related parameters for transit distances up to at least 30 km. The model predicts maximum g-to-p conversion rates at the edges of the plumes where the predicted g-to-p conversion rates are comparable to values derived from field measurements. Elsewhere in the plumes the predicted g-to-p conversion rates are about an order of magnitude lower than the average values deduced from field measurements.     

Trace organic compounds in rain—II. Gas scavenging of neutral organic compounds

Concurrent rain and air sampling was conducted for seven rain events in Portland, Oregon during February through to April of 1984. Concentration data are presented for a number of neutral organic compounds for both the rain-dissolved phase and the atmospheric gas phase. The ambient temperature averaged 8°C. Measured gas scavenging ratios ranged from 3 for tetrachloroethene to 10⁵ for dibutylphthalate, and were generally 3–6 times higher than those calculated from Henry's Law constant (H) values at 25°C taken from the literature. This discrepancy was due to the inappropriateness of applying 25°C H data at 5–10°C. Indeed, excellent agreement between the measured and predicted gas scavenging ratios was found for several polycyclic aromatic hydrocarbons for which temperature-dependent H data were available. These results demonstrate that equilibrium between rain and the atmospheric gas phase is attained for non-reactive neutral organic compounds.     

Modeling distributions of air pollutant concentrations—II. Estimation of one and two parameter statistical distributions

In Part I of this series Taylor, Jakeman and Simpson (1986, Atmospheric Environment, 20, 1781–1789) examined the problem of identifying the appropriate distributional form for air pollution concentration data. In this paper we examine the parameter estimation problem. Monte Carlo simulation is used to compare methods for fitting statistical distributions to such data where the distributional form is known. Three methods are investigated for estimating the parameters of the lognormal distribution, two methods for the exponential distribution, three methods for the γ-distribution and four methods for the Weibull distribution. For all distributions and for each method we examine the accuracy with which the upper percentiles of the distribution are evaluated as it is these percentiles which are referred to by air quality standards. For each distribution a simple empirical model, which yields approximations to the relative root mean square error of the percentile estimates against sample size and parameter values, is developed and demonstrated. Thus for each distributional model an estimate of the relative error associated with evaluating high pollutant levels may be readily determined.     

Inventory of aerosol and sulphur dioxide emissions from India. Part II—biomass combustion

A spatially resolved biomass burning data set, and related emissions of sulphur dioxide and aerosol chemical constituents was constructed for India, for 1996–1997 and extrapolated to the INDOEX period (1998–1999). Sources include biofuels (wood, crop waste and dung-cake) and forest fires (accidental, shifting cultivation and controlled burning). Particulate matter (PM) emission factors were compiled from studies of Indian cooking stoves and from literature for open burning. Black carbon (BC) and organic matter (OM) emissions were estimated from these, accounting for combustion temperatures in cooking stoves. Sulphur dioxide emission factors were based on fuel sulphur content and reported literature measurements. Biofuels accounted 93% of total biomass consumption (577 MT yr⁻¹), with forest fires contributing only 7%. The national average biofuel mix was 56 : 21 : 23% of fuelwood, crop waste and dung-cake, respectively. Compared to fossil fuels, biomass combustion was a minor source of SO₂ (7% of total), with higher emissions from dung-cake because of its higher sulphur content. PM_2.5 emissions of 2.04 Tg yr⁻¹ with an “inorganic fraction” of 0.86 Tg yr⁻¹ were estimated. Biomass combustion was the major source of carbonaceous aerosols, accounting 0.25 Tg yr⁻¹ of BC (72% of total) and 0.94 Tg yr⁻¹ of OM (76% of total). Among biomass, fuelwood and crop waste were primary contributors to BC emissions, while dung-cake and forest fires were primary contributors to OM emissions. Northern and the east-coast India had high densities of biomass consumption and related emissions. Measurements of emission factors of SO₂, size resolved aerosols and their chemical constituents for Indian cooking stoves are needed to refine the present estimates.     

The relationship of sulfur emissions to sulfate in precipitation—II. Gas phase processes

A climatological box model is applied to wet deposition of sulfur in eastern North America using the extreme assumption that all wet-deposited sulfates originate in sulfate aerosol. The measured sulfate in precipitation during 1977–1979 constrains the probability that an SO₂ molecule emitted in the eastern United States is oxidized before deposition or outflow from the region to values greater than 0.5 and more likely near 1.0. This result implies that uniform SO₂ emission reductions will produce nearly proportional reductions in wet sulfates originating in those emissions and deposited on land. A similar result was obtained previously using the more likely assumption that oxidation and removal of SO₂ in precipitating clouds is the major source of wet deposition of sulfur. Therefore, it is argued that uniform regional reductions in annual average SO₂ emissions will produce nearly proportional reductions in wet sulfur deposited on land and originating in those emissions. The amount of wet sulfate deposition is demonstrated to constrain the mean scale of transport along air parcel trajectories for the precursor of wet sulfur, whether SO₂ or sulfate aerosol, to values greater than 900 km. An examination of previous microscopic photochemical models indicates that the sulfate aerosol formation rate is roughly proportional to local SO₂ concentrations, an inference which is consistent with the result of the climatological model.     

Dispersion in neutral boundary layer over astep change in surface roughness—II. Concentration profiles and dispersionparameters

This is a comparative study of dispersion in two different simulated boundary layers over homogeneous surfaces and over a step change (small to large roughness) in surface roughness.Hydrocarbon concentration measurements in the homogeneous boundary layers reflect the differences in generated turbulence for the two surfaces. Comparison of the maximum ground-level concentration as a function of stack height shows typically a factor of two increase for the block-roughness boundary layer (BBL) over that of the smoother fine-Sanspray roughness at the same stack height. This same relative difference is also reflected in the distance of C_max from the stack. The increased turbulence of the block-roughness causes the plume to reach the surface quicker and closer to the stack as compared to the fine-Sanspray boundary layer (FBL). This is also reflected in the relative magnitudes of the lateral and vertical Gaussian dispersion parameters for the two cases. However, their variation with distance from the source are similar and can approximately be described by power laws.Dispersion measurements over the step change in roughness show that the effects of the developing internal boundary layer (IBL) are only significant for low stack heights, with the maximum effect seen for the surface release. For the surface release, the concentration profiles initially follow those of the BBL but tend toward those of the fine-Sanspray boundary layer (FBL) within a short distance downwind. The same trend is present in the Gaussian dispersion parameters. However, the ground-level concentrations are apparently not affected because of the compensating effects of reduced mean velocity and increased turbulence within the IBL. The elevated releases show similar behavior but with a much shallower transition region.In the present case, the incident large-scale turbulence disperses the plume to the extent that the addition of smaller-scale turbulence by the second surface roughness is not noticable. Examination of surface lateral profiles and plume centerline profiles show little or no increased dispersion which could be attributable to a continuous fumigation episode.     

Visibility-reducing species in the denver “brown cloud”—II. Sources and temporal patterns

The chemical and optical measurements collected at the General Motors Research Laboratories' site during the 1978 Denver “brown cloud” study are combined with data on energy consumption and emissions, as well as the use of tracer techniques, to estimate the contributions of the various sources to the fine paniculate mass (FPM) and the visual range reduction (VRR). Although no single source dominates either the FPM or the VRR, combustion processes account for over 80% of both. The major contributors to both the FPM and VRR are: motor vehicles, 26 and 27% (diesel trucks, 8 and 12%; light-duty noncatalyst vehicles. 14 and 9%; light-duty catalyst-equipped vehicles, 4 and 5% and tire rubber, negligible and 1%), coal combustion, > 20 and > 25%, and wood burning, 12 and 18%. The remainders of the FPM and VRR are due chiefly to fuel oil and natural-gas combustion and crustal and fly ash material. The motor vehicles and the wood combustion are the principal sources of both elemental and organic carbon particles while the coal combustion is the most important source of paniculate sulfate and nitrate precursors. Essentially, all the carbonaceous particles appear to be primary particles while most of the sulfate appears to be produced by a heterogeneous process. Both heterogeneous and homogeneous (photochemical) mechanisms appear to be producing nitrate, with the photochemical one being more important.     

Atmospheric dispersion and transport within coastal regions—Part II. Tracer study of industrial emissions in the California Delta Region

Eight large-scale atmospheric tracer tests, utilizing CBrF₃ and/or SF₆, were conducted during September, 1976, within the California Delta Region. The purpose of this study was to demonstrate the large-scale application of single and double tracer techniques to the study of pollutant transport and dispersion under complex, coastal meteorological conditions.The resulting tracer data base was comprehensive enough to permit accurate mass balances of the tracer; essentially all of the tracer was accounted for by this analysis. On the average, plumes emitted from the Montezuma Hills during the test periods were transported southeast over Stockton into the San Joaquin Valley. As a result of the steady nature of the winds, the commonly used Hino correction was found to grossly underestimate the hourly averaged tracer concentrations computed from 10-s averaged concentrations.Experimentally determined rates of dispersion were greater than those associated with Pasquill-Gifford dispersion curves. In spite of the complex meteorology and terrain, estimates of tracer concentrations based upon the Gaussian plume model were found to be reasonably accurate.The relationship between the horizontal standard deviation of the wind, σ_θ, and the horizontal dispersion parameter of the plume, σ_y, was found to follow σ_y∼-0.85 xσ_θ, where x is the downwind distance of the plume center. Calculated trajectories and arrival times of air parcels based upon a numerical solution to the two-dimensional mass balance equation were found to be in excellent agreement with the tracer data.     

The chemistry of bulk precipitation at a site in southeast england—II. Relationships between ions and comparison with other sites

This paper contains a statistical analysis of bulk precipitation chemistry of rain falling on the Tillingbourne Catchment, Surrey. Over the years 1978–1981, mean volume-weighted concentrations were: pH, 4.15, 70.8 μeq ℓ⁻¹ H⁺; organic, 2.8 mg ℓ⁻¹; total SO²⁻₄, 80.5 μeq ℓ⁻¹; NO⁻₃, 36.2 μeq ℓ⁻¹; NH⁺₄, 40.9 μeq ℓ⁻¹; Cl⁻ (2 years) 97.4 μeq ℓ⁻¹, rainfall 1067mm. Compared to other sites in the U.K. and elsewhere receiving acid precipitation in this pH is at the low end of the range, but levels of the other ions are moderate. Similar relations apply to deposition. Ion concentrations are highly correlated, especially total SO²⁻₄, NO⁻₃ and NH⁺₄. This group is linked more loosely to pH and organic content, while Cl⁻ does not correlate at all with the other ions, implying a totally different source, probably sea salt. H⁺ ions in rain correlate better with NO⁻₃ than with SO²⁻₄ and regression analysis suggests that almost all the NO⁻₃ is probably associated with nitric acid, whereas only about 57% of the SO²⁻₄ is associated with sulphuric acid. Deposition is approximately related to rainfall by a power law relationship in which the exponent of the equation varies between 0.5 and 0.9. However, it is concluded that an adequate estimate of deposition cannot be obtained from rainfall alone.     

Turbulent diffusion from a point source in stratified and neutral flows around a three-dimensional hill—II. Laboratory measurements of surface concentrations

Towing-tank and wind-tunnel measurements of the concentration distributions on the surface of a hill when a plume impinges from an upwind source are presented. The stability is varied between very stable and neutral. The results are compared with the theories developed in Part I. When the source is below the dividing-streamline height H_D, the plumes impact on the front surface of the hill, yielding surface concentrations nearly the same as would be observed at the plume centerline in the absence of the hill. However, eddying in the wake can cause oscillations in the plume upwind so as to increase the area of impingement and decrease the average concentration. When the source is above H_D, the plume surmounts the hill top, but if it is only slightly above H_D, maximum surface concentrations can again essentially equal those that would be observed at the plume centerline in the absence of the hill. The maximum surface concentration decreases very rapidly with further increases in source height. The location and value of the maximum surface concentrations are found to be extremely sensitive to slight displacements of the source from the stagnation streamline when the source is below H_D. The general assumptions of the potential flow models developed in Part I to provide estimates of surface concentrations on three-dimensional hills are useful.     

Comparative analysis of chemical reaction mechanisms for photochemical smog—II. Sensitivity of EKMA to chemical mechanism and input parameters

The six chemical reaction mechanisms for photochemical smog described in Pan I (Leone and Seinfeld, 1985, Atmospheric Environment 19,437–464) were used to study the effect of input parameters on volatile organic compound (VOC) control requirements needed to meet the National Ambient Air Quality Standard for ozone. The parameters studied were initial VOC composition, dilution rate, post 8-a.m. emissions, base case (present day) O₃ levels, entrainment from aloft of VOC and ozone and initial VOC/NO_x ratio. The Empirical Kinetic Modeling Approach (EKMA) was used to generate ozone isopleths for each chemical mechanism. The VOC control needed to reduce the maximum ozone concentration from some present day value to 0.12 ppm, assuming no NO_x control and a specified initial VOC/NO_x ratio, was calculated using the six chemical reaction mechanisms. The initial VOC/NO_x ratio was found to have the largest effect of all the parameters studied on VOC control requirements. Choice of chemical mechanism, ozone and VOC entrainmem from aloft, base-case ozone and the composition of the initial VOC mixture also had a large effect on predicted control requirements. To reduce the degree of uncertainty in control predictions using EKMA it is necessary to establish as accurately as possible the composition of urban air in early morning. Also, because of the substantial effect the choice of chemical mechanism has on the predicted control requirements using EKMA, it is important that future work continues to be directed toward evaluating candidate chemical mechanisms with respect to their ability to simulate atmospheric smog chemistry.     

Dolomite phosphate rock (DPR) application in acidic sandy soil in reducing leaching of phosphorus and heavy metals—a column leaching study

A column leaching study was designed to investigate the leaching potential of phosphorus (P) and heavy metals from acidic sandy soils applied with dolomite phosphate rock (DPR) fertilizers containing varying amounts of DPR material and N-Viro soils. DPR fertilizers were made from DPR materials mixing with N-Viro soils at the ratios of 30, 40, 50, 60, and 70 %, and applied in acidic sandy soils at the level of 100 mg available P per kilogram soil. A control and a soluble P chemical fertilizer were also included. The amended soils were incubated at room temperature with 70 % field water holding capacity for 21 days before packed into a soil column and subjected to leaching. Seven leaching events were conducted at days 1, 3, 7, 14, 28, 56, and 70, respectively, and 258.9 mL of deionized water was applied at each leaching events. The leachate was collected for the analyses of pH, electrical conductivity (EC), dissolved organic carbon (DOC), major elements, and heavy metals. DPR fertilizer application resulted in elevations up to 1 unit in pH, 7–10 times in EC, and 20–40 times in K and Ca concentrations, but 3–10 times reduction in P concentration in the leachate as compared with the chemical fertilizer or the control. After seven leaching events, DPR fertilizers with adequate DPR materials significantly reduced cumulative leaching losses of Fe, P, Mn, Cu, and Zn by 20, 55, 3.7, 2.7, and 2.5 times than chemical fertilizer or control. Even though higher cumulative losses of Pb, Co, and Ni were observed after DPR fertilizer application, the loss of Pb, Co, and Ni in leachate was <0.10 mg (in total 1,812 mL leachate). Significant correlations of pH (negative) and DOC (positive) with Cu, Pb, and Zn (P?<?0.01) in leachate were observed. The results indicated that DPR fertilizers had a great advantage over the soluble chemical fertilizer in reducing P loss from the acidic sandy soil with minimal likelihood of heavy metal risk to the water environment. pH elevation and high dissolved organic carbon concentration in soils after DPR fertilizer application are two influential factors.