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In this study, attapulgite-supported nano zero-valent iron (nZVI@ATP) was synthesized by a liquid-phase reduction method using active attapulgite (ATP) as raw material, and used for Pb2+ remediation in aqueous solution. To understand the mechanism of Pb2+ removal, various techniques were used to characterize nZVI@ATP. The results showed that spherical nZVI particles were uniformly dispersed on the surface of ATP, and the agglomeration of nZVI particles was significantly weakened. The adsorption performance of nZVI@ATP for Pb2+ was greatly improved compared with that of ATP ore, in which the Fe/ATP mass ratio of 1:2 was the best loading ratio. Under the conditions of a temperature of 25 °C and a pH of 5.00, the initial concentration of Pb2+ was 700 mg/L, and the Pb2+ removal rate of nZVI@ATP was 84.47%. The adsorption of nZVI@ATP to Pb2+ was mainly a spontaneous endothermic reaction of heterogeneous surfaces, and the adsorption rate of nZVI@ATP to Pb2+ was proportional to pH in the range of 2–5.5. The presence of Na+, Mg2+, and Ca2+ can inhibit the removal of Pb2+, and Ca2+ has the strongest inhibition effect on the removal of Pb2+. The removal mechanism of Pb2+ by nZVI@ATP obtained from SEM-EDS, BET, XRD, FTIR and XPS included reduction, precipitation, and the formation of complexes.

Purpose Arsenite and arsenate leaching from iron (hydr)oxides is one major parameter affecting the mobility of arsenic in the natural environment. In the process of arsenic transfer to groundwater, the retention capacity of arsenic by different iron (hydr)oxides needs to be investigated. The aim of this study is to determine the retention capacity of arsenite or arsenate from the ferrihydrite, lepidocrocite, or magnetite-coated sand column in the leaching process as well as the influence factors on leaching. Materials and methods The leaching of arsenite and arsenate from columns loaded with ferrihydrite, magnetite, or lepidocrocite-coated quartz sand was examined, and the influence factors such as pH, phosphate, and humic acid (HA) contents on leaching and retention were also investigated. Results and discussion The retention performance of As(III) and As(V) depended on the type of iron (hydr)oxides: ferrihydrite>magnetite>lepidocrocite. The retention capacities of As(III) and As(V) by amorphous ferrihydrite versus magnetite and lepidocrocite are 3.25, 5.63 (As(III)) and 1.75, 3.65 (As(V)) times higher. The retention capacity of arsenic is largely affected by the pH of leaching solutions. The retention of As(III) by ferrihydrite is efficient in near-neutral or slightly acidic environments. The addition of phosphate or HA significantly affected the leaching and retention. The addition of phosphate severely inhibited the leaching and retention of As(III) and As(V) by ferrihydrite, and the inhibitory effect was more obvious along with the increase of phosphate concentration. The retention of As(III) and As(V) by ferrihydrite was significantly enhanced by the addition of low-dose HA but was inhibited by the addition of excessive HA. Conclusions Retention performance of As(III) and As(V) from a ferrihydrite-coated sand column is greater than a magnetite-or a lepidocrocite-coated sand column, and the influence factors such as pH, phosphate, and HA affect the leaching and retention of As(III) and As(V). The results theoretically underlie the application of iron (hydr)oxide in arsenic pollution control.

Nanoscale zero-valent iron (nZVI) has a high chemical reactivity for heavy metals, but nZVI forms aggregate easily. In this study, a synthesis of sludge biochar supported nanoscale zero-valent iron (nZVI@SBC) by...

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