Preparation of Adsorbents by Pyrolysis of Sludge Mixed With Steel Slag and Study on Adsorption of Chromium Ions in Water

In this study, the dewatered sludge from the sewage plant and the open-hearth steel slag of the steel plant are used as raw materials. As two wastes, they were mixed and pyrolyzed to prepare a composite absorbent. Further, the adsorption mechanism of the adsorbent to chromium ions in the sewage is explored. The pyrolysis reaction behavior of sludge mixed with steel slag was studied by the thermogravimetric analysis technology. SEM, BET, and XPS were used to analyze the specific surface area, pore size distribution, and pore structure characteristics of pyrolysis products, respectively. Moreover, a comprehensive analysis of the adsorbent was carried out for the adsorption mechanism of hexavalent chromium ions. The results show that the addition of steel slag promotes the pyrolysis of the sludge in each stage. When the content of steel slag is 80%, the increases of reaction rate are the most obvious with the largest increase of weight loss rate in each stage. The SEM results show that the enrichment of sludge on metal oxides is enhanced in the high-temperature range (600–700°C). Besides, when the content of steel slag is 40–60%, the mixture’s growth rate of the specific surface area can reach 600% and the growth rate of total pore volume can reach 350% (the situations of sludge as the baseline). Regarding the measurement of Cr(VI), the adsorption rate of the steel-slag solution is 50.93% and that of the sludge solution is 69%. However, the adsorption rate can be increased to 95% when the steel slag and sludge were mixed as an adsorption solution. In conclusion, the adsorption mechanism of Cr(VI) by additives is controlled by both physical and chemical processes. The present study provides a theoretical basis and technical support for the scientific and reasonable utilization of sludge and steel slag.

Нефелоксетический эффект в нанокристаллах ZnAl-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=-:Cr-=SUP=-3+-=/SUP=-, обусловленный их размером

ZnAl2O4 nanocrystallites doped with Cr3+ ions with mean sizes ranging from 2 to 16 nm were synthesized by the hydrothermal method. Chromium ions occupy the aluminum positions, which symmetry depends on the crystallite size. The smallest nanocrystals have a much larger unit cell than the bigger ones. The metal to ligand distance increases when the size of the nanocrystals decreases. This causes the nephelauxetic effect, which is for the first time (to our knowledge) observed as a size effect. It was also observed that ZnAl2O4: Cr3+ nanocrystals with size larger than 10 nm possesses the same spectroscopic properties as monocrystal.

Спектрально-люминесцентные свойства стекол системы (Y-=SUB=-1-x-=/SUB=-Yb-=SUB=-x-=/SUB=-)-=SUB=-2-=/SUB=-О-=SUB=-3-=/SUB=--Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=--В-=SUB=-2-=/SUB=-О-=SUB=-3-=/SUB=--SiO-=SUB=-2-=/SUB=- + Cr-=SUB=-2-=/SUB=-О-=SUB=-3-=/SUB=-+Na-=SUB=-2-=/SUB=-О

Fused yttrium-alumoborate glasses doped with ytterbium, silicon, chromium, and sodium were synthesized. The influence of the matrix on the "spectroscopic behavior" of chromium ions and the efficiency of their sensitization of Yb3+ luminescence was established by spectral-luminescence and EPR-studies. It was found that (1) chromium in alkali-free glasses is mainly in the oxidation degree Cr(III) with an appreciable admixture of Cr(IV) and Cr(V), (2) the partial replacement of Al2O3 or B2O3 by SiO2 and Y2O3 by Yb2O3 affects to a different extent the relative concentration of optical centers of chromium ions, (3) the addition of alkali results in the formation of Cr(VI) centers as a result of oxidation of less charged chromium ions and predominantly tetracoordinated Cr4+ and Cr5+, (4) Cr3+ ions make the main contribution to the luminescence sensitization of Yb3+ ions, while Cr4+ ions and to a lesser extent Cr5+ play the role of luminescence quencher and internal filter. Sensitization of Yb3+ luminescence through the charge transfer band in Cr(VI) was found. An alkaline glass doped with Cr and Yb upon excitation through the sensitizer produced a luminescence quantum yield of 32% and the conditions for its enhancement were considered. It is shown that the temperature quenching of luminescence of CrYb-containing glasses is significantly lower than that of Cr-containing glasses.

Poly(vinyl chloride)-supported triazoles grafted onto calix[4]arene for chromium ions extraction

A new suitable material was synthesized using click reaction between dialkynyl-p-tert-butylcalix[4]arene and poly(vinyl chloride) azide (PVC-N3). This novel dialkynyl-p-tert-butylcalix[4]arene with triazole groups grafted onto PVC polymer (PVC-0.75CX[4]) has an excellent extraction capability for chromium ions from aqueous solutions. It shows a unique ability to extract chromium (VI) ions from aqueous solutions, thanks to the soft cavity, the presence of π-triazole rings and hydrogen bonds. Cr (VI) ion sorption capacity is 95.5% at pH = 3.