Transformation of As and Cd associated with Fe-Mn-modified biochar during simultaneous remediation on the contaminated soil.

Here, Fe- and Mn-modified biochar (BC-Fe-Mn) was applied to simultaneously stabilize As and Cd in the contaminated soil. The removal efficiencies for NaHCO3-extractable As and DTPA-extractable Cd by BC-Fe-Mn were 60.8% and 49.6%, respectively. The speciation analyses showed that the transformation to low-crystallinity Fe-bound (F3) As, Fe-Mn oxide-bound (OX) of Cd, and residual As and Cd was primarily attributed to stabilizing the two metal(loid)s. Moreover, the correlation analyses showed that the increase of As in F3 fraction was significantly and positively associated with the increase of OX fraction Mn (r = 0.64). Similarly, OX fraction Cd was increased notably with increasing OX fraction Fe (r = 0.91) and OX fraction Mn (r = 0.76). In addition, a novel dialysis experiment was performed to separate the reacted BC-Fe-Mn from the soil for intensively investigating the stabilization mechanisms for As and Cd by BC-Fe-Mn. The characteristic crystalline compounds of (Fe0.67Mn0.33)OOH and Fe2O3 on the surface of BC-Fe-Mn were revealed by SEM-EDS and XRD. And FTIR analyses showed that α-FeOOH, R-COOFe/Mn+, and O-H on BC-Fe-Mn potentially served as the reaction sites for As and Cd. A crystalline compound of MnAsO4 was found in the soil treated by BC-Fe-Mn in the dialysis experiment. Thus, our results are beneficial to deeper understand the mechanisms of simultaneous stabilization of As and Cd by BC-Fe-Mn in soil and support the application of the materials on a large scale.

Adsorption behavior of lead, cadmium, and arsenic on manganese-modified biochar: competition and promotion.

Biochar adsorption of heavy metals has been a research hotspot, yet there has been limited reports on the effect of heavy metal interactions on adsorption efficiency in complex systems. In this study, the adsorbent was prepared by pyrolysis of rice straw loaded with manganese (BC-Mn). The interactions of Pb, Cd and As adsorption on BC-Mn were systematically studied. The results of the adsorption isotherms for the binary metal system revealed a competitive adsorption between Pb and Cd, resulting in decreased Pb (from 214.38 mg/g to 148.20 mg/g) and Cd (from 165.73 mg/g to 92.11 mg/g). A notable promotion occurred between As and Cd, showing an increase from 234.93 mg/g to 305.00 mg/g for As and 165.73 mg/g to 313.94 mg/g for Cd. In the ternary metal system, Pb inhibition did not counteract the promotion of Cd and As. Furthermore, the Langmuir isotherm effectively described BC-Mn's adsorption process in monometallic, binary, and ternary metal systems (R2 > 0.9294). Zeta and FTIR analyses revealed simultaneous competition between Pb and Cd for adsorption on BC-Mn's -OH sites. XPS analysis revealed that As adsorption by BC-Mn facilitated the conversion of MnO2 and MnO to MnOOH, resulting in increased hydroxyl radical production on BC-Mn's surface. Simultaneously, Cd combined with the adsorbed As to form ternary Cd-As-Mn complexes, which expedited the removal of Cd. These results help to provide theoretical support as well as technical support for the treatment of Pb-Cd-As contaminated wastewater.

Dual functional sites strategies toward enhanced heavy metal remediation: Interlayer expanded Mg-Al layered double hydroxide by intercalation with L-cysteine.

The discharge of toxic heavy metals poses a serious threat to human health and environment. The existing water purification systems are lack of promising materials for rapid, efficient, and cost-efficient remediation of numerous toxic heavy metals. Herein, we report on the development of L-cysteine (Cys) intercalated Mg-Al layered double hydroxide (MgAl-LDH/Cys) with a loose lamellar porous architecture as an efficient and economically viable adsorbent for Pb(II) and Cd(II) removal. The intercalation with Cys creates dual functionality, i.e., the interlayer expansion accelerates the diffusion of heavy metals, while Cys acts as additional capture sites for heavy metals. Therefore, remarkable high maximum sorption capacities of 279.58 and 135.68 mg g-1 for Pb(II) and Cd(II) were obtained for MgAl-LDH/Cys compared to those for pristine MgAl-LDH (30.15 and 36.77 mg g-1). MgAl-LDH/Cys exhibits also much faster sorption kinetics in comparison with MgAl-LDH. Such enhancements are attributed to the intercalation of the chelating agent Cys in the MgAl-LDH interlayer channels. Moreover, it is proposed that the adsorption mechanisms involve the isomorphous replacement of Mg sites by Cd(II) forming CdAl-LDH, the precipitation of PbS and CdS, and the chelation of sulfhydryl, carboxyl and amine groups toward Cd(II). Altogether, its facile and environmentally friendly fabrication, ultrahigh sorption efficiencies, and rapid kinetics demonstrate that MgAl-LDH/Cys has potential for practical applications in heavy metal remediation.

Iron-doped hydroxyapatite for the simultaneous remediation of lead-, cadmium- and arsenic-co-contaminated soil.

Since lead, cadmium and arsenic have completely opposite chemical behaviors, it is very difficult to stabilize all these three heavy metals simultaneously. Herein, a novel iron-doped hydroxyapatite composite (Fe-HAP) was developed via an ultrasonic-assisted microwave hydrothermal method for the simultaneous remediation of lead-, cadmium-, and arsenic-co-contaminated soil in Hunan Province, South China. Using DTPA/sodium bicarbonate extractant to extract bioavailable Pb, Cd and As in soil after Fe-HAP remediation for 60 days, the immobilization efficiencies were 79.77%, 51.3% and 37.5% for Pb, Cd and As, respectively. The soil extractable and exchangeable fractions of Pb, Cd and As decreased significantly. In batch experiments, the adsorption kinetics of Pb, Cd and As on Fe-HAP were well described by pseudo-second-order models, indicating that the adsorption is controlled by chemisorption. In the Langmuir adsorption isotherm, the maximum adsorption capacities of Cd2+ and As(V) were 476.2 mg g-1 and 195.69 mg g-1, respectively, while Pb2+ fit the Freundlich model better. The XRD, SEM and XPS analyses indicated that Fe-HAP formed stable minerals of Pb5(PO4)3OH, Cd3(PO4)2·4H2O, Cd(OH)2 and Fe3(AsO4)2·6H2O with Pb, Cd and As. Overall, its facile and efficient immobilization performance indicate that Fe-HAP has potential for practical applications in integrative remediation of Pb-, Cd-, and As- co-contaminated soil.

Complete F-type mitochondrial genome of Chinese freshwater mussels Lamprotula gottschei.

Lamprotula gottschei (Von Martens, 1894) is one of the freshwater pearl mussels which have great meaning on economy in China. The complete F-type mitochondrial genome of L. gottschei was firstly determined. This circle genome (15,915 bp in size) comprises 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, except for COI, CYTB, ND4, ND6 and ND4L, with ATA start codon, the remaining protein-coding genes initiated with the orthodox ATG start codon. There were 25 non-coding regions found throughout the mitogenome of L. gottschei, ranging in size from 1 to 305 bp, the largest of which is between ND2 and tRNA(Gln) (305 bp), and is longer than the control region sequences (about 280 bp) of freshwater mussels from Poland and South Korea. Strictly maternal inheritance (SMI) of mitochondrial DNA (mtDNA) is the standard rule in nearly all anisogamic organisms (SMI), (Roze et al., 2005; White et al., 2008). However, bivalves of the marine family Mytilidae and Veneroida as well as the freshwater family Unionidae possess two independently inheritance mode of mitochondrial DNA (mtDNA) (Boyle & Etter, 2013), which involves maternal (F) and paternal (M) transmission routes concomitant with highly divergent gender-associated mtDNA genomes. This system of mtDNA transmission was called doubly uniparental inheritance (DUI) (Zouros, 2000).