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Journal of Hazardous Materials 132 (2006) 111–117 Soil desiccation rate integration into e ssa S to G IEES NC 2 la 608 en St mber 2006 Abstract Dust cons he wo of the availa ants thereby redu gy th the average desiccation rate is formulated. This is combined with soil characteristics, stressor (environmental and possibly vehicle) characteristics and liquid content in soil to estimate potential emission factors. Using this methodology, the dust suppression potential of aqueous polyethylene oxide (PEO) solution was investigated experimentally with Na-montmorillonite (Na-mmt) as the model dust-generating material. PEO with a molecular weight of 8 × 106 and at aqueous concentrations ranging from 0.5 to 10 g/L, was mixed with 10 g of Na-mmt (surface area = 31.82 ± 0.22 m2/g) and desiccated fo ◦ to distilled w into the form © 2005 Else Keywords: Po 1. Introdu 1.1. Neces Dust is sphere fro cause healt especially i [1] reporte 2.5 could b of people to ment. Gene fall within t ter), and ca have been p ∗ Correspon E-mail ad 0304-3894/$ doi:10.1016/j r 700 h in a specially designed chamber at 25 C and 30% relative humidity. The results show that generally, aqueous PEO is superior ater as a dust suppressant for Na-mmt at concentrations in the range of 0.5–2.0 g/L. The experimental data obtained are introduced ulated estimation methodology, and potential emissions of dust from PEO-admixed Na-mmt are determined. vier B.V. All rights reserved. lyethylene oxide (PEO); Dust; Desiccation; Emission factor; Dust suppressant; Na-montmorillonite ction sity for dust control defined as fine soil that is transmitted to the atmo- m ground sources. Soil-derived anthropodust can h problems such as asthma and some forms of cancer, f the dusts are laden with contaminants. Peters et al. d that human exposure to fine particles such as PM- e the cause of frequent hospital admissions and visits the emergency room for heart and lung disease treat- rally, fugitive dust comprises particles that primarily he PM-10 range (particles of 10�m or less in diame- n have very diverse mineralogy. Several studies [2–5] erformed to characterize the geochemistry of dusts, ding author. Tel.: +1 704 687 4936; fax: +1 704 687 3115. dress: sbae@uncc.edu (S. Bae). often, with the objective of determining their source. Cancado and Peres [5] found quartz, iron oxides and muscovite to be the major mineral phases in dust generated by mining operations in the Iron Quadrangle region of Brazil. Fuel-derived lead (Pb), a legacy of industrial activities in all countries and the use of leaded gasoline in many develop- ing countries until the last decade or so, is commonly found in dust. Lead fallout rates from dust in Raipur City, India ranged from 0.0065 to 0.4304 kg km−2 yr−1 [6]. Particle size scaling performed by Sullivan [7] indicates that dust particles cover the range from clay to silt (0.01–100�m, exceeding PM-10 in coarseness) thereby presenting opportunities for the attachment of contaminants to dust through a range of physico-chemical phenomena. Among these phenomena are cation exchange on clays, and adsorption on both silt and clay. Indeed, it is conceiv- able that the finer particles of dust present the greater human health risk as inhalable dust with respect to the presence of adsorbed contaminants. An investigation of the mutagenicity of urban particulate matter in Bologna, Italy by Pagano et al. [8] – see front matter © 2005 Elsevier B.V. All rights reserved. .jhazmat.2005.11.088 models for polymer suppre unyoung Bae a,∗, Hilary I. Inyang a, T.C. De Bri a Global Institute for Energy and Environmental Systems (G 9201 University City Boulevard, Charlotte, b Universidade Federal de Minas Gerais, Av. Contomo, 842-Sa c School of Arts and Sciences, Benedict College, 1600 Hard Received 3 September 2005; received in revised form 1 Nove Available online 25 January titutes an environmental and human health menace in many regions of t bility of fine soil particles for entrainment in air as dust. Dust suppress cing dust emission factor. Herein, a dust emission estimation methodolo mpirical dust emission nt evaluation alva˜o b, Godwin E. Mbamalu c ), University of North Carolina, 8223-0001, USA , 30110-060 Belo Horizonte, Brazil reet, Columbia, SC 29204, USA 2005; accepted 9 November 2005 rld. The rate of soil desiccation is a significant determinant such as polymer solutions can reduce soil desiccation rate, at involves the integration of desiccation time curves to find 112 S. Bae et al. / Journal of Hazardous Materials 132 (2006) 111–117 mer m indicated th ticle size an Fugitive roads, and exposed to mining ope 1000–1500 sphere [9]. exemplified where such mobile acc 1.2. The ro Liquids cles. The g of the film bind soil p liquid film may not be inadequate be overcom cles into th exposed gr Experim rates [10–1 uid retentio ground cov as vehicula action. In a to be related soil. Then a generation occurrence favor dust faces or ma the focus o n is desic akin osp supp req n rap eous ng th ation ion i nerg ng du biod mic ndin iffic ir to rticle d pro Fig. 1. An idealized schematic illustration of the binding action of poly e existence of inverse proportionality between par- d mutagenic activity in airborne particulate matter. dust can be generated by vehicular action on unpaved wind action on the ground surface at sites that are weather elements by agricultural, construction, and rations. It is estimated that each year, as much as metric tons of fugitive dust is entrained in the atmo- Dust storms are common in regions of dry climate, by the southwestern areas of the United States, storms frequently reduce visibility and cause auto- idents. le of liquid retention in dust suppression can be held as thin films in tension around soil parti- reater the amount of liquid, the greater the thickness s that surround the soil particles. These films can articles together. Even when the thickness of these s is diminished by soil desiccation processes, dusts pressio retard face, m the atm a dust may be water i as aqu reduci applic reduct in the e and lo toxic, Che surrou more d from a soil pa tic; an immediately generated if particle uplift forces are . The forces of interaction among soil particles must e by uplift forces before entrainment of soil parti- e atmosphere as dust can occur. As the airflows over ound, tiny particles are dislodged and moved. ental observations and models of dust generation 4] indicate that dust generation is favored by low liq- n in soil, high content of clay and silt in soil, sparse erage and high intensity of stressing processes such r action, material processing operations and wind nother study [15], dust generation potential was found inversely to moisture and organic content of exposed potentially successful approach to suppressing dust from the source material must be one that inhibits the of one or more of the conditions or processes that release from trafficked and/or exposed ground sur- terial piles. For exposed ground surfaces, which are f this paper, one of the practical options of dust sup- idealized, s presented i may becom sphere as d retention o Usually, th mers suppr provide som 2. Analyti 2.1. The es roadways The ent when the li the adhesi olecules on clay platelets within a clay clod. frequent wetting of the ground surface with liquids to cation that would eventually powder the ground sur- g soil particles readily available for entrainment into here as dust. In dry climates, water is usually used as ressant. Unfortunately, many applications of water uired. The cost of energy and labor to frequently spray id drying situations is quite high. Liquid binders such solutions of lime, and polymers can be effective in e drying rate of soil and thus requiring less frequent of suppressant on exposed surfaces. Even a small n drying rate can produce a very significant decrease y and labor costs of dust suppression over large areas ration. However, any material selected must be non- egradable and inexpensive. al dust suppressants reduce dust in a variety of ways: g and adhering to adjacent particles, thereby making it ult to dislodge them; attracting and trapping moisture keep the surface moist; adhering to and cementing s; acting as a clay dispersant to make clay more plas- ducing heavy agglomerizations of fine particles. An chematic illustration of this possible phenomenon is n Fig. 1. The resulting agglomerates of soil particles e too heavy to be uplifted and entrained in the atmo- ust. Chemical suppressants may provide long-lasting f liquid and offer effective cohesion of soil particles. ey provide a durable water-resistant surface. Poly- ess dust by cementation of soil particles and may e control against moisture change. cal approach timation of dust emission factors for unpaved rainment of particles into the atmosphere may occur ft forces on the particles imposed by airflow exceeds on force between particles and the surface that S. Bae et al. / Journal of Hazardous Materials 132 (2006) 111–117 113 Table 1 Constant for a and b of Eqs. (1) and (2), which is provided by US EPA [16] Constant k (lb/VMT) a b c d generates t on the parti ticles. Then uplift poten particles es generate th in some cas ticularly th surfaces th Dust em (1). This em produces e particulate traveled (V Ef = k ( P 12 where Ef is tiplier for p by US EPA of surface (tons). Eq. for estimat by light du Ef = k ( Ps 12( where Vv i stant, and P The consta Table 1. T particle siz Ps, Wv, an adjusting th 2.2. Analy From pr high liquid to dust gen desiccation from a liqu illustrated i (3) for intr chem nera ng t issi (3) r uid des A e− , A i q. ( uid c ided he av ∫ tf ti Pm (tf − ti) = ∫ tf ti A e−Bt dt (tf − ti) = A ∫ tf ti e−Bt dt (tf − ti) A[−e−Btf + e−Bti ] B(tf − ti) (4) nstants A and B can be obtained from experimental data as liquid content (%) versus drying time of soil samples, e time at the end of the drying experiment (h), ti is the the beginning of the experiment (h), Pmi represents liquid t (%) at the initial time and Pmf is the liquid content (%) end of the experiment (%) as illustrated in Fig. 2. When Industrial roads (Eq. (1)) Public roads (Eq. (2)) PM-2.5 PM-10 PM-30 PM-2.5 PM-10 PM-30 0.23 1.5 4.9 0.27/0.26 1.8/1.7 6.0/6.4 0.9 0.9 0.7 1/0.8 1/0.8 1/1 0.45 0.45 0.45 NA NA NA NA NA NA 0.2/0.2 0.2/0.2 0.3/0.4 NA NA NA 0.5/1 0.5/1 0.3/1 hem. The airflow which imposes a bending moment cle replaces the moment of adhesion force on the par- , the particles roll and become airborne. Only when tial of particles is less than the adhesiveness can the cape from the surface. While wind action alone can e lift necessary to entrain particles in the atmosphere, es, vehicular action induces the lift forces. This is par- e case on unsurfaced roads and other exposed ground at are trafficked by vehicles. ission potential can be assessed through the use of Eq. pirical equation is adapted from US EPA [16] and stimates of dust emission in pounds of size-specific material from an unpaved source, per vehicle mile MT) as follows: s )a( Wv 3 )b (1) the emission factor (lb/VMT), k is particle size mul- article size range and units of interest which is given , a and b are empirical constants, Ps is silt content material (%), and Wv is the weight of mean vehicle (2), adapted from US EPA [16] is amenable to use ing dust emission rates for traffic that is dominated ty vehicles on publicly accessible roads )a( Vv 30 )d Pm 0.5 )c (2) s the mean vehicle speed (mph), d is empirical con- m is the moisture content of surface material (%). nts for a, b, c, d of Eqs. (1) and (2) are shown in hese numbers are specific to different aerodynamic es such as PM-10 and PM-2.5. The parameters of d Pm are source characteristics and can be used for e emission estimates to local conditions. Fig. 2. S dust ge for doi dust em Eq. The liq ing the Pm = Herein when E age liq Pm div vides t period Pma = = The co plotted tf is th time at conten at the tical approach adopted in this research evious experimental work [17–20], it was noted that loss rates during soil desiccation processes can lead eration. However, for an extended time period of in the field, it is important to use an average value id retention curve such as the one that is schematically n Fig. 2. The average value can be estimated using Eq. oduction into Eq. (2) for use in computing potential Pm given b for estimat Ef = k ( ( A[− 0 From Eq. control dus atic illustration of liquid retention during desiccation process. tion rates. This analysis focuses on the methodology his and incorporating the results into a reformulated on model. epresents the liquid loss pattern in a desiccating soil. content, Pm (%), shows an exponential decrease dur- iccation period Bt (3) s the slope of exponential curve, and B is the constant 3) is linearized. Pm can be considered to be the aver- ontent during the desiccation period. The integral of by duration of soil drying experiment (tf − ti) pro- erage liquid content, Pma (%), during the desiccation y Eq. (4), is substituted into Eq. (2), the final equation ion of the emission factor is derived as Eq. (5) Ps 12 )a( Vv 30 )d e−Btf+e−Bti ] .5B( tf−ti) )c (5) (5), three variables are the major parameters that t emission: silt content of surface material; weight 114 S. Bae et al. / Journal of Hazardous Materials 132 (2006) 111–117 of mean vehicle; and liquid content of surface material. Pos- sible control options are vehicle restriction, surface improve- ment, and s traffic on u sion rate b designed, s unpaved ro of surface practically. other two c into two t Through w liquids, roa Chemicals able chang surface. 2.3. Estim conditions In orde paper, form parameters clay during Pl = Wt − W where Pl is the wet sol of dry solid If the p solution ve known to f half-life (t1 of the final ln(Qt) = ln In Eq. (7), is initial qu rate consta From the s obtained. T PEO soluti from the ra t1/2 = 0.69 k′ 3. Materia The use tion is dem experiment tions. Thes The method suppressan Being that at various levels under controlled environmental conditions, an opportunity is provided to use this method to determine the liq- entio t of t Eqs. ment ality s inte btain he e ment xper rder loss ber lled. lowi loss ring ions. ents roce ater mm cogn logi eces cant esid ent rese bia, ourc earch hers ate , 3.3 K2O P2 tion with ge c d) w r. (– rodu solub ngto nfig ndin een was er. urface treatment. The volume and type of vehicular npaved road or mean vehicle speed may alter emis- ut are difficult to enforce. For road surfaces that are ilt content is dependent on soil mix design. Many ad surfaces are not designed. Consequently, control soil particle size distribution has limited potential Control of liquid content is more feasible than the ontrol approaches. Surface treatments can be divided ypes: wet suppression and chemical stabilization. atering or use of aqueous solutions or concentrated d surfaces may be kept wet to control emissions. in solution or concentrated forms can produce desir- es in the physical characteristics of the exposed soil ation of liquid duration under environmental r to indicate how liquid loss is analyzed in this ulations for estimating rate constants from measured are presented as Eqs. (6)–(8). Liquid retention by desiccation processes can be determined as follows: Ws s × 100 (6) the liquid retention by clay (%), Wt is the weight of id (clay + liquid) at time t (g), and Ws is the weight (g). lot of the natural log of the final quantity of PEO rsus time gives a straight line, then the desiccation is ollow first-order kinetics. The rate constant, k′, and /2) can be determined from the plot of the natural log quantity of PEO solution versus desiccation time (Q0) − k′t (7) Qt is the final quantity of liquid in the sample (g), Q0 antity of liquid in the sample (g), k′ is desiccation nt (g/h), and t is the duration of the desiccation (h). lope of linear equation, the rate constant, k′, can be he half-life, which is the time required for half of the on to evaporate from the wet soil, can be calculated te constant as follows: 3 (8) ls and methods of this approach to estimate dust emission reduc- onstrated herein, using the results of desiccation s on clay material with PEO at various concentra- e materials are used for illustrative purposes only. ology is intended for use in evaluating any liquid dust t when once the desiccation rate that applies is known. the clay is expected to retain liquids introduced to it uid ret impac using experi portion variou is to o ering t assess 3.1. E In o liquid a cham contro the fol liquid loss du condit surem using p 3.2. M Na- it is re minera ered n signifi tion. B to easy in this Colum is the s by res researc same m Al2O3 0.53% 0.049% The ca (Na+) exchan metho vendo PEO cally p water- (Warri The co gen bo It has b water polym n value for each aqueous PEO concentration. The he liquid retention on dust emission can be estimated (2)–(5). It should be noted that the purpose of the al section of this paper is not to determine the pro- of liquid retention to PEO aqueous concentration at rmediate desiccation time instants. The focus herein desiccation trend lines for each concentration, cov- ntire desiccation period for use in demonstrating the methodology developed and presented. iment design and rationale to control the environmental parameters that affect from wet soils, desiccation tests were performed in in which temperature and relative humidity could be Aqueous concentrations of PEO were produced at ng concentrations: 0.5, 1, 2, 3, 4, 6, 8, 10 g/L. Free was determined through measurements of weight sample drying, under the controlled environmental PEO solutions were also characterized through mea- of their solution viscosities and dielectric constants dures briefly outlined below. ials tested and justifications of their selection t was used in this research as the model soil although ized that real soils contain a wider distribution of es and particle sizes. The use of Na-mmt was consid- sary because it is common in soils and can produce textural responses that can impact upon dust genera- es, as a clay material, its fine particles are amenable rainment in air as dust. The Na-mmt that was used arch was obtained from the University of Missouri- Missouri Clay Minerals Repository. The repository e of well-characterized clays that are frequently used ers nation-wide. This provides the opportunity for to compare the results of their investigations on the rials. The Na-mmt consists of 62.9% SiO2, 19.6% 5% Fe2O3, 3.05% MgO, 1.68% CaO, 1.53% Na2O, , 0.32% FeO, 0.111% F, 0.090% TiO2, 0.05% S, O5, 0.006% MnO, and the rest is loss on ignition. exchange capacity (CEC) is 76.4 meq/100 g. Sodium minor amounts of calcium (Ca2+) is the principal ation. The surface area (using nitrogen adsorption as measured at 31.82 ± 0.22 m2/g as provided by the [–CH2CH2O–]n–) is a neutral polymer and is typi- ced as a clear solid powder. It is a hard and waxy le polymer. PEO was supplied by Polysciences, Inc. n, PA) and has a molecular weight of 8,000,000. uration of the PEO molecule indicates that hydro- g is likely the means of attachment of PEO onto clay. used as a retention aid for high-yield pulps. Distilled used in all the experiments as the solvent for this S. Bae et al. / Journal of Hazardous Materials 132 (2006) 111–117 115 3.3. Test protocols 3.3.1. Cha Ten gram and transfe ter × 145 m that is sensi for 1 day. A an environ Bryant Ma at 25 ◦C an then made liquid from were made in weight b the envelop liquid loss ing (desicc concentrati 3.3.2. Mea The vis rate at whi that polym ent viscosit research to results. Th rotational v each test, a a polystyre up to the g cosity was stabilized r were perfo solutions. regards phy soil solids t textural