Terephthalaldehyde–Phenolic Resins as a Solid-Phase Extraction System for the Recovery of Rare-Earth Elements

Rare-earth elements (REEs) are involved in most high technology devices and have become critical for many countries. The progress of processes for the extraction and recovery of REEs is therefore essential. Liquid–solid extraction methods are an attractive alternative to the conventional solvent extraction process used for the separation and/or purification of REEs. For this purpose, a solid-phase extraction system was investigated for the extraction and valorization of REEs. Ion-exchange resins were synthesized involving the condensation of terephthalaldehyde with resorcinol under alkaline conditions. The terephthalaldehyde, which is a non-hazardous aromatic dialdehyde, was used as an alternative to formaldehyde that is toxic and traditionally involved to prepare phenolic ion-exchange resins. The resulting formaldehyde-free resole-type phenolic resins were characterized and their ion-exchange capacity was investigated in regard to the extraction of rare-earth elements. We herein present a promising formaldehyde and phenol-free as a potential candidate for solid–liquid extraction REE with a capacity higher than 50 mg/g and the possibility to back-extract the REEs by a striping step using a 2 M HNO3 solution.

Nitrogen source recovery from mature leachate via heat extraction technology: An engineering project application

Large pool of ammonia in mature leachate is challenging to treat with a membrane bioreactor system to meet the discharge standard for pollution control of municipal solid waste landfills in China (GB 16889-2008) without external carbon source addition. In this study, an engineering leachate treatment project with a scale of 2,000 m3/d was operated to evaluate the ammonia heat extraction system (AHES), which contains preheat, decomposition, steam-stripping, ammonia recovery, and centrifuge dewatering. The operation results showed that NH3-N concentrations of raw leachate and treated effluent from an ammonia heat extraction system (AHES) were 1,305–2,485 mg/L and 207–541 mg/L, respectively. The ratio of COD/NH3-N increased from 1.40–1.84 to 7.69–28.00. Nitrogen was recovered in the form of NH4HCO3 by the ammonia recovery tower with the introduction of CO2, wherein, the mature leachate can offer 37% CO2 consumption. The unit consumptions of steam and power were 8.0% and 2.66 kWh/m3 respectively, and the total operation cost of AHES was 2.06 USD per cubic leachate. These results confirm that the heat extraction is an efficient and cost-effective technology for the recovery of nitrogen resource from mature leachate.