Solvent Extraction Purification Research Articles

Особенности экстракционной сернокислотно-фторидной технологии переработки ниобий- и танталсодержащего сырья

The results of researching of the leaching of niobium- and tantalum-containing raw materials by solutions of hydrofluoric and sulfuric acids are presented. Researching have been carried out on the solvent extraction purification and separation of niobium and tantalum from their fluoride-sulfuric acid solutions to obtain niobium oxides and tantalum oxides of the required quality using octanol-1 as an extractant. The possibility of recycling waste technological sulphate-fluoride solutions with the production of magnesium sulfate heptahydrate is shown. Information on the work on the use of pyrohydrolysis as a reagentless method for the isolation of products and the regeneration of hydrofluoric acid is presented.

Leaching and solvent extraction purification of zinc from Mehdiabad complex oxide ore

An integrated hydrometallurgical process was used for the zinc leaching and purification from a zinc ore containing 9.75 wt% zinc. The zinc minerals in the ore were hemimorphite, willemite, and calcophanite. Main gangue minerals were quartz, goethite, hematite, and calcite. Central composite design (CCD) method was used to design leaching experiments and the optimum conditions were found as follows: 30% of solid fraction, 22.05% sulphuric acid concentration, and the leaching temperature of 45 °C. The PLS containing 35.07 g/L zinc, 3.16 g/L iron, and 4.58 g/L manganese impurities was produced. A special purification process including Fe precipitation and Zn solvent extraction was implemented. The results showed that after precipitation of iron, Zn extraction of 88.5% was obtained with the 2 stages extraction system composed of 30 vol% D2EHPA as extractant. The overall Zn recovery from the ore was 71.44%. Therefore, an appropriate solution containing 16.6 g/L Zn, 0.05 g/L Fe, and 0.11 g/L Mn was prepared for the electro-winning unit without using the roasting and calcination steps (conventional method), which result in environmental pollution.

Application of a hydroxylamine nitrate stability model to plutonium purification process equipment

A mathematical model that predicts hydroxylamine nitrate (HAN) (NH2OH·HNO3) stability is applied to aqueous solutions containing HAN, nitric acid and plutonium that are used in plutonium purification processes. The model estimates the stability of these solutions with respect to the rapid, hazardous, autocatalytic reaction of HAN with nitric acid that generates heat and gas. It also accounts for reaction kinetics, temperature changes, gas generation rates, solution volumes and flow rates, and distribution of plutonium and nitric acid between aqueous and organic phases. The model is applied to three typical process vessels used in solvent extraction purification of plutonium – a countercurrent aqueous/organic plutonium stripping column, an oxidation column used for HAN and hydrazine destruction, and a plutonium rework tank. Both normal and off-normal process scenarios are modeled. Two of the off-normal scenarios lead to the rapid autocatalytic reaction of HAN with nitric acid where heat and gas are generated and that could lead to damage of the process equipment and/or release of hazardous plutonium solution from the vessel. In these two cases, stationary aqueous solutions containing HAN, Pu(III), and nitric acid were allowed to slowly react until conditions for the autocatalytic reaction were reached.

Model for predicting hydroxylamine nitrate stability in plutonium process solutions

A mathematical model is described that may be used to determine the safety of hydroxylamine nitrate (HAN) solutions used in solvent extraction purification of plutonium. The most significant hazard associated with hydroxylamine use in processing plutonium is its rapid, autocatalytic reaction with nitric acid which can result in an explosion or pressurization of process vessels with radiological consequences to humans. In addition, heat is produced by the reaction that could potentially ignite process solvents. The HAN decomposition reaction can occur only under specific process conditions (temperature; HAN, plutonium and nitric acid concentrations) and the model is used to identify these conditions so that they can be avoided. A kinetics model has been developed using all of the known significant reactions that could occur in process solutions containing HAN and nitric acid as well as plutonium and iron. The reaction kinetics data (rate laws, rate constants, activation energies) used in the model were obtained from chemical literature sources. The model shows that the autocatalytic HAN reaction with nitric acid is very rapid and is catalyzed by Pu(III) and Fe(II) in process solutions. High temperatures and nitric acid concentrations also promote the reaction.

Rapid measurements of neptunium oxidation states using chromatographic resins

The Savannah River Site’s (SRS) H-Canyon facility uses ceric ammonium nitrate (CAN) to separate impure neptunium (Np) from a nitric acid feed stream containing 0.5–1.0 M concentrations of iron, sodium and sulfate impurities. The material is processed using a two-pass solvent extraction purification which relies on CAN to oxidize Np to Np(VI) during the first pass prior to extraction. Spectrophotometric oxidation-state analyses normally used to validate successful oxidation to Np(VI) prior to extraction were compromised by this feed stream matrix. Therefore, a rapid chromatographic method to validate successful Np oxidation was developed using Eichrom Industries’ TRU and TEVA® resins. The method was validated and subsequently transferred to existing operations in the process analytical laboratories.

Froth flotoextraction, a new method of metal separation from aqueous solutions

A new method of extraction and separation of metals from aqueous solutions, referred to as `froth flotoextraction', is proposed. This method combines two well-known processes: solvent extraction and froth flotation. Extraction is performed by an organic acid extractant at pH values characteristic for each metal, froth is formed by the extract, air bubbles transport the extract phase to the froth and at the same time mix the solution. The method combines high productivity and low cost of flotation with selectivity and low residual metal content of solvent extraction. An equation describing phase separation efficiency is proposed and used for optimization of the process. The method is tested and used in the industrial technology of water recycling in a Russian chemical plant. The final operations of the technology are solvent extraction purification of two froth products containing zinc and copper to produce their sulphates of `chemically pure' grade and flotation decontamination of the recycling water from the residual extractant.

Radiolytic Instability of Ferrous Sulfamate in Nuclear Process Solutions

The radiolytic oxidation of Fe(II) and the destruction of sulfamic acid (SA) in feed solutions for solvent extraction purification of 237Np and 238Pu from spent nuclear fuels have been investigated...