We have investigated 128 14 C-dated ordinary chondrites from Oman for macroscopically visible weathering parameters, for thin section-based weathering degrees, and for chemical weathering parameters as analyzed with handheld X-ray fluorescence. These 128 14 C-dated meteorites show an abundance maximum of terrestrial age at 19.9 ka, with a mean of 21.0 ka and a pronounced lack of samples between 0 and 10 ka. The weathering degree is evaluated in thin section using a refined weathering scale based on the current W0 to W6 classification of Wlotzka (1993), with five newly included intermediate steps resulting in a total of nine (formerly six) steps. We find significant correlations between terrestrial ages and several macroscopic weathering parameters. The correlation of various chemical parameters including Sr and Ba with terrestrial age is not very pronounced. The microscopic weathering degree of metal and sulfides with newly added intermediate steps shows the best correlation with 14 C terrestrial ages, demonstrating the significance of the newly defined weathering steps. We demonstrate that the observed 14 C terrestrial age distribution can be modeled from the abundance of meteorites with different weathering degrees, allowing the evaluation of an age-frequency distribution for the whole meteorite population.

Producing a P fertilizer from sewage sludge ash (SSA) is a strategy to efficiently recycle P from a secondary raw material. The P speciation in four SSAs was characterized before and after the removal of heavy metals by a thermo-chemical treatment that involved CaCl addition. We chose complementary techniques to determine the direct P speciation, including X-ray powder diffraction, solid-state P direct-polarization magic-angle spinning nuclear magnetic resonance, and X-ray absorption near edge structure. Results from these techniques were compared with operational and functional speciation information obtained from a sequential P extraction and a plant biotest with Italian ryegrass grown on a soil-sand mixture with little available P. The speciation of P in untreated and thermo-chemically treated SSAs depended on their elemental composition. At a molar ratio of Ca:P ≤ 2, SSAs contained combinations of polymorphs of AlPO, β-tricalcium phosphate, and apatite-like P species. In SSAs with a molar ratio of Ca:P > 2, an apatite-like molecular environment was predominant. The thermo-chemical process induced an increase in crystalline phases and enhanced the crystallinity of the P species. The structural order of the bulk sample was the most decisive parameter in controlling the P availability of the studied SSAs to plants. We conclude that, to produce a high-quality fertilizer and despite of the successful heavy metal removal, the thermo-chemical process requires further development toward enhanced P bioavailability.

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An innovative full-scale implementation of a permeable reactive barrier, consisting of a double-row of cylinders filled with zerovalent iron shavings, for chromate remediation was monitored over four years. Solid samples were analyzed to elucidate (i) the relevant corrosion mechanisms and products, (ii) the pathways of chromate reduction and immobilization, and (iii) the long-term performance of the barrier situated in a hydrological and geochemical complex groundwater regime. Sampling and analysis of groundwater and reactive material revealed an oxidative iron corrosion zone evolving in the inflow and a zone of anaerobic iron corrosion in the center and outflow of the barrier. Chromate reduction was mainly confined to the inflow region. The formation and thickness of corrosion rinds depended on sampling time, position, and depth, as well as on the size, shape, and graphite content. In the inflow, the corrosion rinds mostly consisted of goethite and ferrihydrite. X-ray absorption fine structure spectroscopy revealed two distinct Cr III species, most likely resulting from homogeneous and heterogeneous redox reaction pathways, respectively. The longevity and long-term effectiveness of the PRB appears to be primarily limited by reduced corrosion rates of the ZVI-shavings because of the thick layers of Fe-hydroxides.

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