Field site leaching from recycled concrete aggregates applied as sub-base material in road construction.

The release of major and trace elements from recycled concrete aggregates used in an asphalt covered road sub-base has been monitored for more than 4 years. A similar test field without an asphalt cover, directly exposed to air and rain, and an asphalt covered reference field with natural aggregates in the sub-base were also included in the study. It was found that the pH of the infiltration water from the road sub-base with asphalt covered concrete aggregates decreased from 12.6 to below pH 10 after 2.5 years of exposure, whereas this pH was reached within only one year for the uncovered field. Vertical temperature profiles established for the sub-base, could explain the measured infiltration during parts of the winter season. When the release of major and trace elements as function of field pH was compared with pH dependent release data measured in the laboratory, some similar pH trends were found. The field concentrations of Cd, Ni, Pb and Zn were found to be low throughout the monitoring period. During two of the winter seasons, a concentration increase of Cr and Mo was observed, possibly due to the use of de-icing salt. The concentrations of the trace constituents did not exceed Norwegian acceptance criteria for ground water and surface water Class II.

Charge-based fractionation of oxyanion-forming metals and metalloids leached from recycled concrete aggregates of different degrees of carbonation: a comparison of laboratory and field leaching tests.

The release and charge-based fractionation of As, Cr, Mo, Sb, Se and V were evaluated in leachates generated from recycled concrete aggregates (RCA) in a laboratory and at a field site. The leachates, covering the pH range 8.4-12.6, were generated from non-carbonated, and artificially and naturally carbonated crushed concrete samples. Comparison between the release of the elements from the non-carbonated and carbonated samples indicated higher solubility of the elements from the latter. The laboratory leaching tests also revealed that the solubility of the elements is low at the "natural pH" of the non-carbonated materials and show enhancement when the pH is decreased. The charge-based fractionation of the elements was determined by ion-exchange solid phase extraction (SPE); it was found that all the target elements predominantly existed as anions in both the laboratory and field leachates. The high fraction of the anionic species of the elements in the leachates from the carbonated RCA materials verified the enhanced solubility of the oxyanionic species of the elements as a result of carbonation. The concentrations of the elements in the leachates and SPE effluents were determined by inductively coupled plasma mass spectrometry (ICP-MS).

Optimization of an anion-exchange high performance liquid chromatography-inductively coupled plasma-mass spectrometric method for the speciation analysis of oxyanion-forming metals and metalloids in leachates from cement-based materials.

A method was developed for the speciation analysis of the oxyanions of As(III), As(V), Cr(VI), Mo(VI), Sb(III), Sb(V), Se(IV), Se(VI) and V(V) in leachates from cement-based materials, based on anion-exchange HPLC coupled with ICP-MS. The method was optimized in a two-step multivariate approach: the effect of sample pH and mobile phase composition on resolution, peak symmetry and analysis time was studied. Optimum conditions were then identified for the significant experimental factors by studying their interdependence. A mobile phase composition of 20 mM ammonium nitrate, 50 mM ammonium tartrate and pH 9.5 was found to be a compromise optimum for the separation of the target analytes using isocratic elution. The optimum condition provided separation of the analytes in less than 6 min, at a mobile phase flow rate of 1.0 mL/min. The signal intensities of the analytes were improved by adding 1% methanol to the mobile phase. The limit of detection of the method was in the range 0.2-2.2 µg/L for the various species. The effect of sample constituents was studied using spiked concrete leachates. The method was used to determine the target oxyanionic species in leachates generated from a concrete material in the pH range 3.5-12.4; CrO(4)(2-), MoO(4)(2-) and VO(4)(3-) were detected in most of the leachates.

Overcoming matrix interferences in ion-exchange solid phase extraction of As, Cr, Mo, Sb, Se and V species from leachates of cement-based materials using multiple extractions.

Solid phase extraction (SPE) methods based on multiple extractions have been developed to overcome matrix interferences in the charge-based fractionation analysis of As, Cr, Mo, Sb, Se and V leached from cement-based materials. Disposable SPE tubes packed with 500 mg strong anion-exchange (SAX) or strong cation-exchange (SCX) sorbents were used to extract the anionic and cationic species of the elements, respectively. The multiple extractions were based on the percolation of a small sample volume (5.0 mL) through a series of identical ion-exchange tubes. For most of the elements, more than 90% of the anionic species were extracted from a sample containing up to 16 g L(-1) NO(3)(-) by passing the aliquot through five identical SAX tubes. Percolating a sample aliquot through three identical SCX cartridges gave more than 99% retention for Cr(III) from leachates containing a high concentration of interfering metal cations. The anionic and cationic analytes showed only slight non-specific adsorption on the SCX and SAX sorbents, respectively, except for V(V) on the SCX sorbent. A condition was established for the quantitative elution of the retained analytes from the ion-exchange sorbents with 1.0 mol L(-1) HNO(3). The multiple ion-exchange SPE procedures were validated using spike recovery tests. The methods were used to determine the anionic and cationic fractions of the target elements in concrete leachates covering a broad range of pH (3.8-13.4). The elements were found to exist predominantly as anions in the alkaline and neutral leachates. A high fraction (85%) of cationic Cr was detected in the most acidic leachate (pH 3.8).

Fractionation analysis of oxyanion-forming metals and metalloids in leachates of cement-based materials using ion exchange solid phase extraction.

A simple and versatile solid phase extraction (SPE) method has been developed to determine the anionic species of As, Cr, Mo, Sb, Se and V in leachates of cement mortar and concrete materials in the pH range 3-13. The anionic fractions of these elements were extracted using a strong anion exchanger (SAX) and their concentrations were determined as the difference in element concentration between the sample and the SAX effluent. Inductively coupled plasma mass spectrometry (ICP-MS) was used off-line to analyse solutions before and after passing through the SAX. The extraction method has been developed by optimizing sorbent type, sorbent conditioning and sample percolation rate. Breakthrough volumes and effect of matrix constituents were also studied. It was found that a polymer-based SAX conditioned with a buffer close to the sample pH or in some cases deionised water gave the best retention of the analytes. Optimal conditions were also determined for the quantitative elution of analytes retained on the SAX. Extraction of the cement mortar and concrete leachates showed that most of the elements had similar distribution of anions in both leachate types, and that the distribution was strongly pH dependent. Cr, Mo and V exist in anionic forms in strongly basic leachates (pH>12), and significant fractions of anionic Se were also detected in these solutions. Cr, Mo, Se and V were not determined as anions by the present method in the leachates of pH<12. Anionic As and Sb were found in small fractions in most of the leachates.

Fractionation and determination of aluminum and iron in soil water samples using SPE cartridges and ICP-AES.

The use of commercially available solid phase extraction (SPE) cartridges for the fractionation of Al and Fe in soil water is described. The quantitative determination was done by inductively coupled plasma atomic emission spectrometry (ICP-AES). Different types of SPE cartridges, based on cation exchange, anion exchange, and chelation were studied. To avoid pH changes, the SPE cartridge should be conditioned with a buffer that has a pH close to that of the sample. Both strong cation exchange (SCX) and chelation were found to work well, whereas low recovery was observed for Al when anion exchange was used. For Fe, the sum of the anionic and cationic fractions that passed through the cartridges was nearly 100%. The results obtained for Al for 23 soil water samples using a SPE/SCX cartridge and ICP-AES were compared with equilibrium calculations using the program ALCHEMI and also with a fractionation method that was based on separation on a manually prepared SCX column and detection by molecular spectrophotometry, after complexation with pyrocatechol violet (SCX-PCV method). The SPE/SCX-ICP-AES results for the labile Al fraction (Al bound to the SCX cartridge) showed an acceptable correlation with the results obtained by the equilibrium calculations, except for the samples with the highest DOC concentrations, whereas the values obtained for labile Al by the more traditional SCX-PCV method were much lower. We recommend that the SPE/SCX-ICP-AES procedure described in this work be selected for the fractionation of Al and Fe species in soil and freshwater samples.