A selective hydrometallurgical method for scandium recovery from a real red mud leachate: A comparative study.

The aim of this study was to recover Sc as the main product and Fe as a by-product from Hungarian bauxite residue/red mud (RM) waste material by solvent extraction (SX). Moreover, a new technique was developed for the selective separation of Sc and Fe from real RM leachates. The presence of high Fe content (∼38%) in RM makes it difficult to recover Sc because of the similarity of their physicochemical properties. Pyrometallurgical and hydrometallurgical methods were applied to remove the Fe prior to SX. Two protocols based on organophosphorus compounds (OPCs) were proposed, and the main extractants were evaluated: bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP). The results showed that SX using diethyl ether and tri-n-octylamine (N235) was efficient in extracting Fe(III) from the HCl leachate as HFeC14. Over 97% of Sc was extracted by D2EHPA extractant under the following conditions; 0.05 mol/L of D2EHPA concentration, A/O phase ratio of 3:1, pH 0-1, 10 min of shaking time, and a temperature of 25 °C. Sc(OH)3 as a precipitate was efficiently obtained by stripping from the D2EHPA organic phase by 2.5 mol/L of NaOH with a stripping efficiency of 95%. In the TBP system, 99% of Sc was extracted under the following conditions: 12.5% vol of TBP, an A/O phase ratio of 3:1, 10 min of shaking time, and a temperature of 25 °C. The Sc contained in the TBP organic phase could be efficiently stripped by 1 mol/L of HCl with a stripping efficiency of 92.85%.

Effect of long retention time in the settler on phosphorus removal from communal wastewater.

GOALS: The objective of the paper is to illustrate the solution of a chronic problem occurring in a wastewater treatment facility with a capacity of 12,000 inhabitant equivalent. A drastic phosphorus concentration increase (two or three times higher than the Hungarian limit of 1 mg/l) was observed in the wastewater treatment facility for a long time (12-24 h) with changing time periods indicating malfunctioning in the operation of the facility. METHODS: Computer-aided simulation technique was used to develop a solution for the treatment of the problem using a software developed by the Department of Environmental and Chemical Engineering, University of Veszprém, Hungary. RESULTS AND DISCUSSION: The simulation studies show that if the nightly inflow is less than 200 m3/h at least for two hours, the system doesn't then receive enough fresh nutrients which can cause a deficiency in the nutrient uptake of the PAOs in the anaerobic zones. This can result in the fact that the PAOs accumulate less phosphorus into the aerobic zones. CONCLUSION: Long retention time (10 h) is the reason for the problem, namely--under special conditions--the phosphorus in the sludge of the settling tank of the wastewater treatment plant. The problem was caused by phosphorus dissolution from the sludge of the settling tank during the undesirably long retention time.