Selective Dissolutions Research Articles

Dissolution and Electrodeposition of Rare Earth Oxides within Acidic Eutectic Solvents

The dissolution and separation of rare earth metals from their oxides represent a global demand due to the multifunctional applications of rare earths across various fields, necessitating expedited research in their extraction and recovery. The development of functional solvents such as ionic liquids and deep eutectic solvents solubilizing these metal oxides has gained interest in the recent years. In this study, various carboxylic acids as the active component in eutectic solvents are investigated in terms of the solubilization and electrodeposition of rare earths. Specifically, the solubility of lanthanum oxide reaching up to 0.38 M was achieved, as determined by the ICP-OES. A higher selectivity towards the lighter lanthanum oxide as compared to the heavier neodymium oxide was obtained, thus presenting a significant opportunity for selective dissolutions. Spectroscopic techniques including UV-vis molecular absorbance, ATR-FTIR, and NMR were employed to elucidate the speciation of the dissolved metal oxides and the solvation environment. Further, the electrodeposition of the solubilized rare earths directly in these media was studied on Cu to assess the ability to electrodeposit metals under benign conditions. This presentation will highlight electrolyte development for selective separation and direct utilization of the solubilized rare earths as elecrodeposits.

Transformation of crystalline and short-range order minerals in a long-term (47 years) rice-rice cropping system

The effect of long-term fertilizer and manure applications on short-range order (SRO) and crystalline mineral transformation was studied in a 47-year puddled rice-rice cropping system experiment in Odisha, India. The relationship of SRO minerals with phosphorus and potassium fixation capacity and soil carbon fractions was also evaluated. Soils from different treatment combinations of farmyard manure (FYM), nitrogen (N), phosphorus (P) and potassium (K) were separated in two ways: (i) removal of binding materials (ii) non-removal of binding materials (ultrasonic vibration), followed by fractionation of the contents into silt and clay. All crystalline minerals, SRO minerals, P and K fixation were measured in silt and clay. The X-ray diffractograms of clays (<2 μm) were recorded in Philips Diffractometer (model PW 1710). Selective dissolutions of SRO minerals were carried out by extraction with sodium hydroxide, acid ammonium oxalate, dithionite-citrate-bicarbonate and sodium pyrophosphate. The results showed that the soils were composed of kaolin (49.6–54.4%), mica (32.7–39.0%) and smectite (10.6–17.0%). The clay-size mica loses its crystallinity and becomes finer after the addition of fertilizers and manure during intensive rice cultivation. The content of amorphous ferri-aluminosilicate varied from 8.0 to 16.23 g 100 g−1 in clay and 1.49–3.38 g 100 g−1 in silt. The plots treated with NP + FYM had the highest total oxalate extractable oxide in both clay and silt. Application of FYM increased ferrihydrite in both clay and silt. Potassium fixation was higher in plots skipped with the long-term application of K. Formation of SRO minerals was positively affected by nutrient stress caused by the omission of one or more nutrients. SRO minerals in the rice soil did not have a major effect on the fixation of K and P; rather, it is controlled by the fertilizer and FYM application. However, carbon fractions had a significant positive correlation with SRO minerals.

Investigation of the decomplexation of polyamide/CaCl2 complex toward a green, nondestructive recovery of polyamide from textile waste

AbstractThe ‘circular economy’ concept envisages deriving the maximum value out of resources and reducing waste to a minimum. In textiles, that includes the recovery of fiber materials out of used clothing and reusing them in the construction of new clothes. Processes such as mechanical separation, depolymerization treatment, and selective dissolutions of individual polymers are applied. We investigate the approach of selective nondestructive dissolution and recovery of polyamide fiber from mixed textile waste by using the solvent system CaCl2/ethanol/water (CEW) based on complexation and decomplexation of polyamide (PA). The results show that PA is precipitated and decomplexed by simple addition of water and a substantial amount of previously incorporated calcium by complexation, is removed. The recovered polyamide shows properties similar to pristine polyamide. Investigation on a mixed textile waste model of polyamide/wool demonstrates that CEW treatment can successfully separate different fiber materials. The nondestructive approach in dissolving PA using CEW, clearly shows the benefit, that PA fiber can be separated by controlled complexation/decomplexation without degradation, thus avoiding the repolymerization step. Furthermore, the solvent system is made of abundantly available materials that are inexpensive and used widely in industrial‐scale operations. Thus, the concept will make significant contribution to a green textile recycling approach.

Bi-continuous porous structures from the selective dissolution of ionic solid solutions

Bi-continuous porous metal evolves from the selective dissolution of an alloy, a process known as dealloying. Here we report a similar observation in the selective dissolution of NaCl from a NaCl-AgCl solid solution. A procedure of simultaneous quenching and dissolution that retains the homogeneity of the solution is designed with the help of small-angle neutron scattering. The process in water creates bi-continuous porous AgCl of smooth ligaments and pores ~300 nm wide, which can coarsen up without altering the bi-continuous morphology. Post-mortem elemental analysis identifies a NaCl-compositional threshold at 35%, below which no dissolution occurs, a critical behavior suggestive of the need for percolating dissolution pathways. The work reveals intriguing similarities between the selective dissolutions of metallic and ionic solid solutions, bridging their mechanisms and promising new ways of fabricating functional porous materials.

Bi-Continuous Porous Structures from the Selective Dissolution of Ionic Solid Solutions

Bi-continuous porous metal evolves from the selective dissolution of an alloy, a process known as dealloying. Here we report a similar observation in the selective dissolution of NaCl from a NaCl-AgCl solid solution. A procedure of simultaneous quenching and dissolution that retains the homogeneity of the solution is designed with the help of small-angle neutron scattering. The process in water creates bi-continuous porous AgCl of smooth ligaments and pores ~300 nm wide, which can coarsen up without altering the bi-continuous morphology. Post-mortem elemental analysis identifies a NaCl-compositional threshold at 35%, below which no dissolution occurs, a critical behavior suggestive of the need for percolating dissolution pathways. The work reveals intriguing similarities between the selective dissolutions of metallic and ionic solid solutions, bridging their mechanisms and promising new ways of fabricating functional porous materials.

Examining mineral-associated soil organic matter pools through depth in harvested forest soil profiles.

Mineral-associated organic matter is associated with a suite of soil minerals that can confer stability, resulting in the potential for long-term storage of carbon (C). Not all interactions impart the same level of protection, however; evidence is suggesting that C in certain mineral pools is dynamic and vulnerable to disturbance in the decades following harvesting. The objective of this research was to describe and characterize organic matter-mineral interactions through depth in horizons of soils of contrasting stand age. Sequential selective dissolutions representing increasingly stable mineral-associated organic matter pools from water soluble minerals (deionized water), organo-metal complexes (Na-pyrophosphate), poorly-crystalline minerals (HCl hydroxylamine), and crystalline secondary minerals (Na-dithionite HCl)) were carried out for Ae, Bf and BC horizons sampled from a Young and Mature forest site (35 and 110 years post-harvest) in Mooseland, Nova Scotia, Canada. Sequential selective dissolution extracts were analyzed for C, δ13C, iron (Fe) and aluminum (Al). Organo-metal complexes (OMC) were the largest mineral-associated OM pool in all horizons. This pool dominated the C distribution in B horizons (~60–70% of Bf bulk C), with a minor contribution from poorly-crystalline (PCrys), crystalline (Crys) minerals and water soluble (WS) associations. C in OMC and PCrys pools explained the variation in bulk C in horizons through depth at both sites. Twice as much C in OMC pools was measured at the Mature site compared to the Young site in the Bf horizons, supported by higher C:(Fe+Al) ratios. Isotopic analysis indicated that this extraction procedure isolated distinct mineral-associated OM pools. δ13C signatures of pyrophosphate-extracted OMC pools ranged from -27‰ to -28‰, similar to δ13C of bulk C and to plant-derived humic acids and associated biomass. The water soluble phase (mean δ13C = -29 ‰) was up to 2 ‰ more depleted, whereas the δ13C of Crys pools were more enriched in 13C (-13‰ to -16 ‰) compared to bulk soil. The results from this study suggest that association with minerals does not necessarily confer stability: organo-metal pools dominate in podzol horizons through depth, and contribute most to C storage, but are potentially susceptible to destabilization following the physical changes resulting from forest harvesting disturbance.

Mineralogy, magnetic susceptibility and geochemistry of Fe-rich Oxisols developed from several parent materials

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.

Soil Evolution and Mass Flux of Basaltic Cinder Cones in a Cool, Semi‐Arid Climate

Core Ideas Soil development across a chronosequence of basaltic cinder cones. Elemental mass balance data were used to investigate secondary mineral formation. Elucidate rates and processes of early stage weathering. Soil developmental processes on young volcanic cinders in cool, semiarid climates are not well understood and previously under‐studied, but present a unique setting within which to study neoformation of soils under well‐dated time constraints. This study investigates the development of physical, chemical, and mineralogical soil properties on a chronosequence of basaltic cinder cones, aged approximately 2.1, 6.9, and 13.9 ka, at Craters of the Moon National Monument and Preserve in southern Idaho. Representative parent material, coarse fragments, and soil samples were analyzed using selective dissolutions and total elemental digests. Elemental mass balance data were used together with the soil physicochemical data to investigate weathering and secondary mineral formation within each soil profile. The highest degree of weathering was identified on the 13.9 ka profile, followed by the 6.9 and 2.1 ka soils. Short‐range ordered minerals, including allophane and ferrihydrite, dominate the colloidal fraction of all soils, with greatest proportions in the oldest soil. Dominant soil‐forming processes documented along the chronosequence of basalt‐derived soils are the accumulation of organic carbon, weathering of rock fragments, loss of base cations, redistribution of Fe, Al, and Ti, and the accumulation of secondary short‐range order and crystalline minerals. This study provides critical information to elucidate rates and processes of early stage weathering, dust influence, and soil evolution on cinders in cool and dry climates.

Pedogenic iron oxides in soils of the Acre State, Brazil

ABSTRACT: Iron oxides are environmental indicators and influence on physical and chemical behavior of soils. This research aimed to identify and characterize pedogenic iron oxides in soils of the Acre state, Brazil. The soils developed from sedimentary rocks of the Solimões Formation. Twenty one samples of subsurface horizons were collected from ten soil profiles. Soil samples were analyzed by x-ray diffractometry associated to selective chemical dissolutions. Fe contents in the clay minerals (Fes), in the pedogenic iron oxides (Fed) and in the poorly crystalline oxides (Feo) were determined. The Al3+-substitution and the mean crystal diameter of goethite and hematite were estimated. Soils presented low contents of Fes and Fed. The Fed/Fes ratio indicated soils in the intermediate stage of weathering, with dominance of goethite, hematite and maghemite. This condition of weathering was confirmed by the higher frequency of goethites and hematite with intermediate Al3+-substitution. Goethites have isodimensional forms and hematite have flat plaques forms.

A sequential selective dissolution method to quantify storage and stability of organic carbon associated with Al and Fe hydroxide phases

Stabilization of SOM (soil organic matter) is regulated in part by sorption and desorption reactions happening at mineral surfaces, as well as precipitation and dissolution of organo-metal complexes. Fe and Al hydroxides play a particularly significant role in SOM stabilization in soils due to their ubiquitous distribution and their highly reactive surface properties. Iron and Al hydroxides exist in soils across a wide spectrum of crystallinity, ranging from dissolved Fe and Al cations which combine with organics to form organo-metal precipitates to the more crystalline end members, goethite and gibbsite, which sorb SOM through a variety of molecular interactions. Though the importance of these sorption and precipitation reactions has long been recognized, the distribution of SOM among Fe and Al hydroxides of differing crystallinity has not been well quantified, nor has the timescale over which these stabilization mechanisms operate. In an attempt to measure the distribution of organic C among (i) Al- and Fe-humus complexes (ii) short-range-order (SRO) Al and Fe hydroxide surfaces and (iii) crystalline Fe oxyhydroxide surfaces, a single method combining several selective mineral dissolutions was applied to soils of four different geneses (a tropical forest Andisol, a temperate forest basaltic Mollisol, a Mediterranean coastal prairie Mollisol, and a northern mixed hardwood forest Spodosol). The traditional reactants used in selective dissolutions were replaced with carbon-free analogues so that the carbon released along with the Fe and Al at each stage of the selective dissolution process could be measured. Selective dissolutions were performed sequentially: Na-pyrophosphate (organo-Al and Fe complexes) followed by hydroxylamine (SRO Al and Fe hydroxides) followed by dithionite-HCl (crystalline Fe hydroxides). Carbon, Al, and Fe concentrations, as well as radiocarbon abundance were measured in the solutions yielded by each stage of the selective dissolution process. Results suggest that precipitation of organo-metal complexes (Na-pyrophosphate extractable C) often accounts for the largest pool of stabilized C among the three selectively dissolved pools, but these complexes were 14C enriched in comparison to C from the other selectively dissolved pools and the residual C left on crystalline mineral surfaces after all three stages of selective dissolution. Hydroxylamine and dithionite-HCl extractable C pools were, on average, small and often below detection level in temperate soils. However, radiocarbon values for these C pools were generally depleted in comparison to other pools. These results suggest variation in organo-mineral complex stability is associated with degree of crystallinity of the mineral phase. Overall, this work suggests that sequential selective dissolution methods are a promising tool for characterizing the content and isotopic composition of soil C associated with distinct organo-mineral and organo-metal associations.

Refined Geomorphologic Interpretation of Glacial Deposits using Combined Soil Development Indices and LiDAR Terrain Analysis

Core Ideas Soil derived information can aid age discrimination of glacial deposits. Profile development indices proved to be an effective tool for age discrimination of glacial deposits. Geomorphic reconnaissance of glacial deposits in forested catchments can be greatly improved by using LiDAR technologies. The ages of glacial deposits in the Lake Tahoe Basin (LTB) have been poorly constrained. Recent absolute cosmogenic dates and a newly delivered light detection and ranging (LiDAR) dataset for LTB, have revived interest for the age interpretation of these glacial deposits. In this study, we combined field geomorphic reconnaissance, terrain analysis, and soil development indices to discern the timing of glaciation for three Quaternary moraine complexes (Meeks Creek, General Creek, and McKinney Creek) in the western LTB. Tahoe‐age deposits displayed significantly more relaxed and wider crests and lower flank slopes than Tioga‐age deposits. However, these parameters cannot resolve the relative ages of Tahoe I from Tahoe II and Tioga I from Tioga II. The interpretation of various soil development indexes combined with terrain analysis improved relative age assignment, especially for Tahoe I and II. Among the best soil parameters for age discrimination were: textural separates, amount of rock fragments, and elemental composition (C, Al, Fe, Si). Other parameters, including sand‐size ratios or soil selective dissolutions, failed to separate relative ages. In addition, we combined multiple soil properties into a soil profile development index (PDI), which clearly showed that soil development tends to increase with age and that this overall trend was independent of the moraine complex. Our results showed that this combined approach can greatly aid moraine age discrimination, especially for these densely forested catchments.

FORMAS DE FERRO, SILÍCIO E, OU, ALUMÍNIO NA GÊNESE DE FRAGIPÃS E HORIZONTES COESOS DOS TABULEIROS COSTEIROS

Na unidade geomorfológica dos Tabuleiros Costeiros dominam os solos com horizontes coesos, e alguns deles têm a presença de horizontes cimentados comumente do tipo fragipã. Esses horizontes interferem na dinâmica da água, no crescimento de raízes e, consequentemente, na nutrição mineral de plantas. O objetivo deste trabalho foi avaliar, por meio da dissolução seletiva, a participação de formas de Fe, Si e, ou, Al na coesão e, ou, cimentação de fragipãs e horizontes coesos em Argissolos e Espodossolos da região dos Tabuleiros Costeiros do sul da Bahia e norte do Espírito Santo. Para isso, foram realizadas extrações seletivas de Fe, Si e Al por ditionito-citrato-bicarbonato de sódio (DCB) e oxalato ácido de amônio. Os maiores teores de Fe, Si e, principalmente, Al extraídos por oxalato de amônio nos fragipãs sugerem que, na gênese desses horizontes, formas de baixa cristalinidade desses elementos agem como cimentantes químicos. As dissoluções seletivas não evidenciaram a participação de formas de alta ou baixa cristalinidade de Fe, Si e, ou, Al na gênese dos horiozontes coesos em solos dos Tabuleiros Costeiros. Os Argissolos Amarelos apresentaram goethitas com alta substituição isomórfica de Fe por Al, condizente com o ambiente de forte intemperização, não redutivo e pH ácido onde esses solos se encontram nos Tabuleiros Costeiros. A substituição isomórfica de Fe por Al nos óxidos de Fe cristalinos apresentaram relação com o grau de cristalinidade e teor de Fe obtido na primeira extração com o DCB.

Transformation of short-range order minerals in maize (Zea mays L.) rhizosphere

Under nutrient stress, low molecular weight organic acids are released in rhizosphere, which dissolve the crystalline layered silicate minerals and subsequently some short range order (SRO) minerals may be formed. To analyze this hypothesis, a controlled greenhouse experiment was conducted with three contrasting soils belonging to Alfisols, Inceptisols and Vertisols order in two phases, viz. Sorghum-sudangrass depletion and test crop experiment on maize. The SROs were measured by selective dissolutions. The results indicate that, NaOH extractable amorphous ferri-alumino silicate was higher in rhizosphere, whereas mild extractant extractable SRO dissolution was increased due to fertilization and rhizospheric effect. Fourier transform infrared band showed changes in 3400&amp;ndash;3600/cm region (adsorbed water) and Si-O stretching vibration (1000/cm). This information will provide a new insight in formation of SROs under the rhizospheric environment.

Availability of geogenic heavy metals in soils of Thiva town (central Greece)

Potentially toxic metals in the urban chemical environment impose risks to both ecosystem and human health. Here, we evaluate the labile pools and availabilities of non-anthropogenic Ni, Cr, Co and Mn in soil samples from Thiva town (central Greece) and investigate their associations with common soil properties and geochemical data obtained by the aqua regia and single selective dissolutions. Experimental work included the initial application of the sequential extraction protocol proposed by the European Community Bureau of Reference and chemical extractions with ethylenediamine tetraacetic acid solution and a modified physiologically based extraction test with the aim to obtain the operationally defined fractions of plant availability and human bioaccessibility, respectively. The leachate results demonstrated that despite the significant contribution of residual metal species especially for Ni and Cr, the studied serpentine soils provide chemically labile pools for all the considered elements. Nickel was found to be the most available metal with the order being Ni > Cr ∼ Co ∼ Mn for plant uptake and Ni > Cr > Co ∼ Mn for human bioaccessibility. The aqua regia extractable concentrations are not predictors of elemental availabilities except for Ni bioaccessible data interpreting however only a moderate percentage of the total variance. The incorporation of basic soil properties (mostly total organic carbon), geochemical data for the major elements Ca, Mg and Fe and ammonium oxalate extractable Cr significantly improved the estimations for individual elements entailing the strong influence of the chemistry and mineralogy of soil materials to the release of focus metals from the soil matrix. This study provides for the first time bioaccessible data for serpentine-derived soils that are more realistic for evaluating potential adverse effects on the human health.

Rietveld quantitative phase analysis of Yeelimite-containing cements

Yeelimite-containing cements are attracting attention for their tailored properties. Calcium sulfoaluminate, CSA, cements have high contents of Yeelimite and they are used for special applications. Belite calcium sulfoaluminate, BCSA or sulfobelite, cements have high contents of belite and intermediate contents of Yeelimite, and they may become an alternative to OPC. Here, we report Rietveld quantitative phase analyses for three commercially available CSA clinkers, one CSA cement, and two laboratory-prepared iron-rich BCSA clinkers. The crystalline phases are reported and quantified. Selective dissolutions are employed for BCSA clinkers to firmly establish their phases. Finally, the overall unaccounted contents (amorphous plus crystalline not quantified) have been determined by two approaches: i) external standard procedure (G-method) with reflection data; ii) internal standard procedure (spiking method with ZnO) with transmission data. The overall unaccounted contents for CSA clinkers were ~10wt.%. Conversely, the unaccounted contents for BCSA clinkers were higher, ~25wt.%.

Determination of vanadium(V) in the particulate matter of emissions and working areas by sequential dissolution and solid-phase extraction

A method based on selective sequential dissolutions is proposed to determine total vanadium(V) in particulate matter of emissions and working areas at concentrations 1,000 times lower than the threshold limit of 0.05 mg m(-3). Separation and preconcentration of vanadium(V) has been achieved by solid-phase extraction on Chelex 100 resin. Possible influence of the matrix has been investigated for two standard reference materials (SRMs), NIST SRM 1648 and BCR-038, before and after spiking, with vanadium(V) recovery in the range 97-103%.

Sources of trace metals in Ferralsols in New Caledonia

SummaryOne third of New Caledonia is occupied by soils deriving from ultrabasic rocks anomalously rich in trace metals such as Cr, Ni, Mn and Co. The location of the metals present in three samples from a toposequence of Ferralsols was studied by combining selective dissolutions (CaCl2, Cu(NO3)2, hydroxylamine, dithionite–citrate–bicarbonate), examinations with a transmission electron microscope (TEM) equipped with an EDAX device, and X‐ray diffraction and infrared spectroscopy. The behaviour of the metals during dissolution was found to depend on both the type of metal and the location of the samples in the toposequence. In the lowland soil samples derived from transported materials, about 50% of total Mn and Co and a small fraction (&lt; 1%) of total Ni were dissolved in the hydroxylamine reagent. By TEM, the manganese oxide minerals present in one of the lowland samples were found to have chemical compositions similar to those of lithiophorite–asbolane mixed layers identified previously in the subsurface horizons of the laterites capping the landscape where the toposequence occurs. Whatever the location of samples, goethite, i.e. the major constituent of these soils, was found to be the scavenger of the largest proportions of Ni and of about 40% of total Cr. However, this mineral was present as two distinct morphological facies, and each of them had a statistically different chemical composition. The small needle‐shaped goethite, which was abundant in the lowland soils only, was richer in Ni and Si and poorer in Al than the larger acicular one. Our data show that the potential mobility of trace metals in these soils is likely to be controlled by the most soluble phases identified, i.e. the Co‐rich Mn oxides and the Ni‐rich needle‐shaped goethites.

Determination of inorganic nickel compounds in the particulate matter of emissions and workplace air by selective sequential dissolutions

A speciation method of inorganic nickel compounds in airborne particulate, based on selective sequential extractions, is described. It allows the separation and the determination of Ni(0), Ni(II) soluble salts such as sulphate and chloride, Ni insoluble compounds such as nickel oxide and sulphide, to which a different toxicity and therefore a different risk are related. The nickel concentration in each fraction was determined by Flame or Furnace Atomic Absorption Spectroscopy. The proposed procedure has been tested first, on synthetic samples prepared with the different nickel compounds, in the presence of atmospherical particulate matter not containing nickel, in order to take into account the possible matrix influence. The speciation was then repeated on four different samples (fly ash deriving from a solid waste incinerator and three RSMS from NIST: Coal Fly ash SRM 1633b, Urban Particulate 1648, Washington Dust 1649), followed by an evaluation of matrix spiking and recovery analyses. Performing multiple analyses of the spiked samples assessed the repeatability of the procedure.

Characterization of molecular heterogeneities of LLDPE by multiple crystallization–dissolution steps

This article demonstrates that a fractionation technique, based on molecular segregation during the crystallization from the melt and dissolution of the crystals, allows a complete characterization of the molecular heterogeneity in the comonomer distribution of linear low density polyethylene. An ethylene–1-hexene copolymer with a bimodal short chain branching distribution has been fractionated by multiple step crystallizations followed by selective dissolutions in tetrachloroethylene. The relative amount of each component of the distribution in each fraction was determined from the melting curves of isothermally crystallized fractions.

Microaggregates from Oxisols and Inceptisols: dispersion through selective dissolutions and physicochemical treatments

In the present work, aggregation of soils containing iron oxides was investigated through dispersion treatments. Microaggregates (0.1–0.2 and 0.2–0.5 mm) of six Oxisols from Brazil and Cameroon and three Inceptisols from Mid-Europe were treated with eleven different dispersing agents and the resulting particle size distribution was measured. Dithionite (DCB), which selectively removes Fe-oxides promoted the highest dispersion. This indicated that Fe oxides participate in aggregation. Treatments with specifically adsorbing anions (citrate, oxalate, bicarbonate, phosphate) disaggregated the samples to different degrees. Citrate alone was almost as effective as DCB although only small amounts of Fe were dissolved. This behaviour was related to an anion specific adsorption on Fe oxides leading to aggregate dispersion. A highly significant correlation was found between degree of dispersion after oxalate treatment and the ratio Si o Fe o . Dispersion by dissolution of surface-active oxides of Fe and Al, by surface charge modification through specific adsorption of anions and disruption of SiOFe bonds are discussed. The dispersive effect of various anions followed approximately its order in adsorption affinity for Fe oxides.