In this study have been compared four types of MnO2 polymorphs in terms of Mn removal from water: three tunnel structures of akhtenskite (AKH), cryptomelane (CRY) and pyrolusite (PYR) and one layered birnessite (BIR). The scope of the presented research included adsorption tests of the influence of material and solution parameters on the efficiency of manganese removal. The MnO2 polymorphs before and after the manganese adsorption (with Mn adsorbate) were characterized by XRD, SEM+EDS and ASAP porosimetry analyses.
AKH was synthesized by using the method described by Zhang et al. (https://doi.org/10.1039/D1RA06025B). BIR, CRY and PYR were prepared using methods described by McKenzie (https://doi.org/10.1180/minmag.1971.038.296.12). After synthesis, the samples were dried at 100 °C and next ground in the agate mortar
The test solution of Mn was prepared according to European Standard EN 13752. The effect of solution properties and MnO2 type on the adsorption of divalent Mn was tested in the range of pH 2–9, ionic strength (I) of 1.0–50 mmol/L, constant initial concentration (Ci) 10 mg Mn/L and contact time 24 h. The ionic strength of the test solution was increased by adding NaCl, and pH was adjusted by NaOH and HCl. The doses of MnO2 were 0.05 g/L (AKH, BIR), 0.2 g/L (CRY) and 1.0 g/L (PYR). All tests were incubated at 10 °C. The experiment was performed in triplicate. After adsorption, the test solution was separated from the MnO2 mixture using MCE 0.22 μm membrane syringe filters. The Mn concentration in the solution was analyzed using a flame atomic absorption spectrometer.
The methodology has been described in detail in the article https://doi.org/10.3390/ijms24054448.
FILES’ DESCRIPTION
1. Title: Mn_adsorption_on…..(.ods) or (.xlsx)
In these files are presented the results of manganese ions adsorption (q) on the raw MnO2 polymorphs: akhtenskite, birnessite, cryptomelane, and pyrolusite respectively. The results of pH measurement before and after adsorption are presented too. The results come from the test with different ionic strengths of solution (1, 5, 10 and 50 mmol/L).
2. Title: SEM…(.tif)
The files present the morphology of the raw MnO2 polymorphs (akhtenskite, birnessite, cryptomelane, and pyrolusite respectively) and the same polymorphs after manganese ions adsorption (Mn adsorbate), obtained using a field emission scanning electron microscope.
3. Title: EDS…(.docx) or (.odt)
The files present the results of the elemental composition of polymorphs’ surfaces analysed using an energy-dispersive X-ray spectroscopy (EDS) detector. The files are related to samples of raw polymorphs and also to polymorphs after manganese adsorption (with Mn adsorbate). In the files are presented microphotographs with marked 3-5 sampling points on the surfaces and the following tables contain the elemental composition.
4. Title: ASAP_porosimetry_results…..(.ods) or (.xlsx)
The files present the results of the low-temperature nitrogen adsorption on polymorphs. The files are related to samples of raw polymorphs and also with polymorphs after manganese adsorption (with Mn adsorbate). In the files are presented the values of nitrogen pressure detected during measurements.
5. Title: XRD…(.xy)
The files present the phase analysis results of polymorphs using an X-ray diffractometer. The files are related to samples of raw polymorphs and also with polymorphs after manganese adsorption (with Mn adsorbate). In the files are presented the values of 2theta angle (x coordinate) and CPS counts per second (y coordinate). It is a text file and it can be opened using a notebook and next exported to other types of software.
(2023-02-22)
