Effects of aging on surface properties and endogenous copper and zinc leachability of swine manure biochar and its composite with alkali-fused fly ash.

Biochar aging is a key factor leading to the decline of biochar stability and the release of endogenous pollutants. This study investigated the effects of five artificial and simulated aging processes on the surface properties and endogenous copper (Cu) and zinc (Zn) leachability of swine manure biochar and its composite with alkali-fused fly ash. Aging obviously reduced carbon (C) content on the surface of swine manure biochar and increased oxygen (O) content. Among all the aging treatments, high-temperature aging had the greatest effect on C content. Following the aging treatments, the C-C bond contents on the surfaces of swine manure biochar decreased significantly, whereas the C-O bonds increased significantly; however, there were less changes in the amounts of C-C and C-O bonds on the surfaces of modified biochar than on swine manure biochar. Aging significantly enhanced the leaching toxicity of Cu and Zn, and Zn availability and bioaccessibility in swine manure biochar and modified biochar. However, it minimized Cu availability and bioaccessibility, especially under high-temperature aging. Greater amounts of Zn than Cu were extracted from swine manure biochar and modified biochar. However, under all the aging treatments, the leaching toxicity, availability, and bioaccessibility of Cu and Zn in modified biochar were significantly lower than in swine manure biochar. This implies that modified biochar application poses lower environmental risks than swine manure biochar.

A novel concept for the biodegradation mechanism of dianionic catechol with homoprotocatechuate 2,3-dioxygenase: A non-proton-assisted process.

The theory of "proton-assisted process" can well explain the catalytic mechanism of homoprotocatechuate 2,3-dioxygenase (2,3-HPCD) with a monoanionic substrate (homoprotocatechuate, HPCA). Here a "non-proton-assisted process" is presented to interpret catalytic mechanism of 2,3-HPCD with a dianionic substrate (4-nitrocatechol, 4NC). The ONIOM calculation is performed to investigate the reaction pathway of a wild-type 2,3-HPCD with 4NC (H200H-4NC system). The catalytic reaction is comprised of four steps: (1) A dioxygen attacks the aromatic ring to produce an alkylperoxo species. (2) O-O bond cleavage and the formation of an epoxide species occur. (3) A seven-membered O-heterocyclic compound is generated by the extinction of the epoxy structure. (4) The seven-membered ring undergoes ring opening to form the final product (C2-C3 cleavage product). The effective free energy barrier of the catalytic reaction of the H200H-4NC system is 26.2 kcal mol-1, which is much higher than that of the H200H-HPCA system. Furthermore, two calculated electronic configurations (Fe(III)-O2•- and Fe(III)-SQ•) have a high similarity to previously detected ones, which demonstrates that the Asn200 variant (H200N-4NC variant system) employs a C4 (para-carbon) pathway to produce a C4-C5 cleavage product. Our findings provide an in-depth understanding of the catalytic mechanisms of dianionic catechol and its derivatives.

Migration and fate of metallic elements in a waste mud impoundment and affected river downstream: A case study in Dabaoshan Mine, South China.

Fate of metallic elements and their migration mechanisms in a waste mud impoundment and affected downstream were assessed. Physicochemical and mineralogical methods combined with PHREEQC calculation, statistical analysis and review of relevant literatures were employed. Results showed that the waste in mud impoundment had been severely weathered and acidized. Metallic elements exhibited high mobility and activity, with a mobility ranking order of Cd > Zn > Mn > Cu ≈ Cr > As ≈ Pb. Hydraulic transportation originating from elevation variation was the most important driving force for metallic elements migration. Although damming standstill was considered as an effective strategy for controlling coarse suspended particulate pollutants, metallic elements were still transported to the Hengshi River in both dissolved phase and fine suspended particle phase accompanied by the overflow of acid mine drainage. The concentrations of dissolved metallic elements were attenuated significantly along the Hengshi River within 41 km stretch. Precipitation/ co-precipitation of iron oxyhydroxides, especially schwertmannite, ferrihydrite and goethite minerals, were established as the most critical processes for metallic elements attenuation in river water. Accompanied by metals migration in the river, two pollution sensitive sites with notably high content of metals in the stretch of S6-S8 and S10, were identified in gently sloping river stretch.

catena-Poly[[diaqua-(2,2'-bipyridine-κN,N')nickel(II)]-µ-biphenyl-2,2'-dicarboxyl-ato-κO:O'].

In the title compound, [Ni(C(14)H(8)O(4))(C(10)H(8)N(2))(H(2)O)(2)](n), the Ni(II) atom is coordinated in a slightly distorted octa-hedral geometry by two water mol-ecules, two N atoms from a 2,2'-bipyridine ligand and two O atoms from the carboxyl-ate groups of two 2,2'-biphenyl-dicarboxyl-ate (2,2'-dpa) ligands. The 2,2'-dpa ligand acts as a bridge between neighbouring Ni(II) atoms, forming one-dimensional coordination polymers along [100]. The coordinated water mol-ecules form hydrogen bonds to the carboxyl-ate O atoms of 2,2'-dpa within the same coordination polymer, and one O-H⋯π inter-action is also formed to 2,2'-dpa.

Bis(µ-biphenyl-2,2'-dicarboxyl-ato)bis-[(2,2'-bipyridine)cobalt(II)].

In the title compound, [Co(2)(C(14)H(8)O(4))(2)(C(10)H(8)N(2))(2)], the Co(II) atom is coordinated by two N atoms from one 2,2'-bipyridine ligand and two O atoms from two biphenyl-2,2'-dicarboxyl-ate (2,2'-dpa) ligands in a distorted planar geometry. Longer Co-O contacts [2.437 (3) and 2.552 (3) Å] are formed to the second O atom of each coordinated carboxyl-ate group so that these groups approximate a bidentate coordination mode and the coordination geometry around Co(II) approaches distorted octa-hedral. The 2,2'-dpa ligands bridge two Co(II) atoms, forming a cyclic dinuclear complex around a centre of inversion.