Optima 2100 dv icp aes

The total concentrations of heavy metals were measured by digesting the dry sludge samples with aqua regia for 180-min reaction time (Dong et al. 2013 (link)). Then the extracts were filtered through 0.22 μm filter membranes before analyzing the total metal content on an ICP-AES instrument (Perkin Elmer Optima 2100 DV ICP-AES). The modified sequential extraction procedure as reported by Aikpokpodion et al. (2013 ) was implemented to analyze the speciation of Cu, Cd, Ni, Cr, and Zn in sludge samples with six steps, which can be presented in sequence: step one, water-soluble fraction (F1); step two, exchangeable fraction (F2); step three, carbonate-bound fraction (F3); step four, Fe-Mn oxides-bound fraction (F4); step five, organic and sulfide-bound fraction (F5); and step six, residual fraction (F6). The details of the modified sequential extraction procedures were reported in our previous study (Zhang et al. 2016 (link)). The mobility factors (MFs) of heavy metals was calculated as the ration between the sum of the water-soluble, exchangeable, and carbonate-bound fractions (F1, F2, and F3) and the total concentration.

The total carbon, hydrogen, and nitrogen contents of BC and nZVI-BC composite were determined using an Elemental analyzer (Elementar Analysensysteme Gmbh, Hanau, Germany). The Fe content in BC and nZVI-BC was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) (Perkin Elmer Optima 2100 DV ICP-AES). Ash contents of the materials were defined as the mass remaining after pyrolysis at 750 °C in a crucible until a constant weight was obtained. Brunauer-Emmett-Teller (BET)-specific surface area was measured using ASAP2020 surface area and porosity analyzer (Micromeritics, Norcross, USA). Scanning electron microscope (SEM, Hitachi 4700 microscope, Hitachi) was used to determine the morphology of the samples. The surface chemistry analysis of the composite was conducted using X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi). Transmission electron microscopy (TEM) analysis was carried out using a JEM-2100F (JEOL, 200 kV) to observe the microstructure of the materials.