Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these material before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials' buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.
The pathways of CaCO3 crystallization are manifold, often involving one or several metastable amorphous or nanocrystalline intermediate phases. The presence of such intermediates is often overlooked, because they are short-lived and/or occur at small molar fractions. However, their occurrence does not just impact the mechanisms and pathways of formation of the final stable CaCO3 phase, but also affects their crystal size, shape, and structure. Here we document the presence of a short-lived intermediate through in situ and time-resolved small and wide-angle X-ray scattering combined with high resolution electron microscope observations. When ikaite forms concomitant with the dissolution of amorphous calcium carbonate (ACC) but prior to calcite formation, fairly large glendonite-type calcite crystals grow despite the presence of citrate ligands that usually reduce crystal size. These were ideal seeding crystals for further crystallization from supersaturated ions in solution. In contrast, in the absence of ikaite the crystallization of calcite proceeds through transformation from ACC, resulting in fine-grained spherulitic calcite with sizes ∼8 times smaller than when ikaite was present. Noteworthy is that the formation of the intermediate ikaite, although it consumes less than 3 mol % of the total precipitated CaCO3, still clearly affected the calcite formation mechanism.
Layered double hydroxides (LDHs) occur naturally and are synthesised for catalysis, drugdelivery and contaminant remediation. They consist of Me(II)-Me(III) hydroxide sheetsseparated by hydrated interlayers and weakly held anions. Often, LDHs are nanocrystalline andsheet stacking and Me(II)-Me(III) arrangement can be disordered, which influence reactivity andcomplicate structural characterisation. We have used pair distribution function (PDF) analysis, toprovide detailed information about local and medium range order (< 9 nm), to determine thestructure of synthetic Fe(II)-Fe(III)/Al(III) LDH. The data are consistent with ordered Me(II)and Me(III) in hydroxide sheets, where structural coherence along the c axis decreases with increasing Al content. The PDF for Fe(II)-Al(III) LDH (nikischerite) is best matched by apattern for a single metal hydroxide sheet. Parallel to decreased structural coherence betweenlayers, coherence within layers decreased to ~6 nm for synthetic nikischerite. Thus, disorderdeveloped within and between the sheets, resulting in mosaic crystals with coherent scatteringdomains decreasing in all directions. The high density of grain boundary terminations wouldaffect reactivity. Based on classical nucleation theory and the Kossel crystal growth model, wepropose that loss of structural coherence stems from increased supersaturation and the presenceof Al-hydroxides during formation of the Al-rich LDH
The effect of organic molecules on CaCO3 crystallization, in particular on the formation of the initial amorphous calcium carbonate (ACC) phase, is poorly understood despite this knowledge being crucial for designing biomimetic compounds with specific function, strength and stability. We monitored ACC crystallization in the presence of varying concentrations of aspartic acid (ASP) and glycine (GLY). We observed an increase in ACC lifetime with increasing amino acid concentrations and showed that the amino acid molecules sorbed onto the ACC particles. However, little if any difference in composition and atomic structure or the so formed ACC was observed. Similarly, the crystallization pathway of ACC via vaterite and calcite although delayed, was only slightly affected by the added amino acids. The only exemption was at the highest tested ASP concentration where ACC formation was inhibited, The calcite crystals that formed in the presence of ASP had rounded edges and rough surfaces, features that are not observed for the pure, inorganic calcite or calcite formed in the presence of GLY. Overall, the results suggest that the amino acids affected ACC lifetime through the inhibition of crystal nucleation and growth, more so in the presence of ASP than GLY.
Biochars
function as electron transfer mediators and thus catalyze
redox transformations of environmental pollutants. A previous study
has shown that bone char (BC) has high catalytic activity for reduction
of chlorinated ethylenes using layered Fe(II)–Fe(III) hydroxide
(green rust) as reductant. In the present study, we studied the rate
of trichloroethylene (TCE) reduction by green rust in the presence
of BCs obtained at pyrolysis temperatures (PTs) from 450 to 1050 °C.
The reactivity increased with PT, yielding a maximum pseudo-first-order
rate constant (k) of 2.0 h–1 in
the presence of BC pyrolyzed at 950 °C, while no reaction was
seen for BC pyrolyzed at 450 °C. TCE sorption, specific surface
area, extent of graphitization, carbon content, and aromaticity of
the BCs also increased with PT. The electron-accepting capacity (EAC)
of BC peaked at PT of 850 °C, and EAC was linearly correlated
with the sum of concentrations of quinoid, quaternary N, and pyridine-N-oxide
groups measured by XPS. Moreover, no TCE reduction was seen with graphene
nanoparticles and graphitized carbon black, which have high degrees
of graphitization but low EAC values. Further analyses showed that
TCE reduction rates are well correlated with the EAC and the C/H ratio
(proxy of electrical conductivity) of the BCs, strongly indicating
that both electron-accepting functional groups and electron-conducting
domains are crucial for the BC catalytic reactivity. The present study
delineates conditions for designing redox-reactive biochars to be
used for remediation of sites contaminated with chlorinated solvents.
Sulfidized nanoscale zerovalent iron (S-nZVI) is an Fe-based reactant widely studied for its potential use for groundwater remediation. S-nZVI reactivity has been widely investigated testing various contaminants in various water matrices, but studies on S-nZVI corrosion behaviour and reactivity upon exposure to complex groundwater chemistries are limited. Here, we show that anoxic aging of S-nZVI for 7 days in the absence and presence of key groundwater solutes (i.e., Cl−, SO42−, Mg2+, Ca2+, HCO3−, CO32−, NO3−, or HPO42−) impacts Fe0 corrosion extent, corrosion product and reduction rates with trichloroethene (TCE). White rust was the dominant corrosion product in ultrapure water and in SO42−, Cl−, Mg2+ or Ca2+ solutions; green rust and/or chukanovite formed in HCO3− and CO32− solutions; magnetite, formed in NO3− solutions and vivianite in HPO42− solutions. The aged S-nZVI materials expectedly showed lower reactivities with TCE compared to unaged S-nZVI, with reaction rates mainly controlled by ion concentration, Fe0 corrosion extent, type(s) of corrosion product, and solution pH. Comparison of these results to observations in two types of groundwaters, one from a carbonate-rich aquifer and one from a marine intruded aquifer, showed that S-nZVI corrosion products are likely controlled by the dominant GW solutes, while reactivity with TCE is generally lower than expected, due to the multitude of ion effects. Overall, these results highlight that S-nZVI corrosion behaviour in GW can be manifold, with varied impact on its reactivity. Thus, testing of S-nZVI stability and reactivity under expected field conditions is key to understand its longevity in remediation applications.
Biochars function as electron transfer mediators and thus catalyze redox transformations of environmental pollutants. A previous study has shown that bone char (BC) has high catalytic activity for reduction of chlorinated ethylenes using layered Fe(II)–Fe(III) hydroxide (green rust) as reductant. In the present study, we studied the rate of trichloroethylene (TCE) reduction by green rust in the presence of BCs obtained at pyrolysis temperatures (PTs) from 450 to 1050 °C. The reactivity increased with PT, yielding a maximum pseudo-first-order rate constant (k) of 2.0 h–1 in the presence of BC pyrolyzed at 950 °C, while no reaction was seen for BC pyrolyzed at 450 °C. TCE sorption, specific surface area, extent of graphitization, carbon content, and aromaticity of the BCs also increased with PT. The electron-accepting capacity (EAC) of BC peaked at PT of 850 °C, and EAC was linearly correlated with the sum of concentrations of quinoid, quaternary N, and pyridine-N-oxide groups measured by XPS. Moreover, no TCE reduction was seen with graphene nanoparticles and graphitized carbon black, which have high degrees of graphitization but low EAC values. Further analyses showed that TCE reduction rates are well correlated with the EAC and the C/H ratio (proxy of electrical conductivity) of the BCs, strongly indicating that both electron-accepting functional groups and electron-conducting domains are crucial for the BC catalytic reactivity. The present study delineates conditions for designing redox-reactive biochars to be used for remediation of sites contaminated with chlorinated solvents.
Chlorinated solvents contaminated soils and aquifers are a widespread problem in industrialized countries and many require clean-up due to the risk of contaminant flow into groundwater systems. Clean-up is costly and often invasive, thus there is high interest in stimulating natural attenuation processes. For this, first an assessment of the type and extent of natural attenuation present at the site is required. Here, we present chemical, isotopic and microbial analyses of waters collected at a chlorinated ethene contaminated site in Denmark to give insights into natural attenuation processes. The data gives indication of complete reductive dechlorination by microbial communities but their extent varies greatly across short distances and between the different geological layers. The data further indicates that overall, chlorinated ethene degradation through natural attenuation is small at this site but near surface degradation due to aerobic co-metabolism or abiotic geochemical reduction could potentially play a role.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
