Efficient adsorption of low concentration rare-earth ions by carbides derived from excess sludge: preparation, performance and mechanism

Abstract

Different carbonization technologies were used for the resource treatment of excess sludge, and different carbonization products were prepared, which were used in the experimental study of adsorption treatment of low-concentration rare-earth wastewater (rare-earth ion concentration 185.70 mg L⁻¹, calculated using REO, which is the mass percentage of rare-earth oxides). The results showed that low-temperature carbides can be used for rare-earth ion adsorption because of their large specific surface area, high strength and good hydrophobicity. Their adsorption effect is the best, and the adsorption rate is 98.77% while the primary desorption rate is 71.41%. Through X-ray fluorescence spectrometry detection, it was found that the main rare-earth ions adsorbed were lanthanum ions and neodymium ions. X-ray diffraction analysis results show that most of the rare-earth ions formed new conjugated compounds and existed in the precipitate. Through FTIR detection, it was found that the hydroxyl radicals, the hydroxyl groups of carboxylic acids, and C–O and C–X (halogens) of the LCS loaded with rare-earth ions underwent stretching vibration. The Brunauer–Emmett–Teller specific surface area test showed that the specific surface area of dry sludge was increased by 69%. SEM and EDS detection showed that there were many conjugates of rare-earth ions in the rough site. It is preliminarily inferred that the adsorption process is a physicochemical process with surface adsorption as the main mechanism and chemical complexation as the secondary mechanism. This study not only provides ideas for the resource utilization of urban excess sludge solid waste but also realizes the efficient recovery of low-concentration rare-earth ions.