Waste Remediation Using in Situ Magnetically Assisted Chemical Separation

Abstract

The magnetically assisted chemical separation process (MACS) combines the selective and efficient separation afforded by chemical sorption with the magnetic recovery of ferromagnetic particles. This process is being developed for treating the underground storage tanks at Hanford. These waste streams contain cesium, strontium, and transuranics (TRU) that must be removed before this waste can be disposed of as grout. The separation process uses magnetic particles coated with either 1) a selective ion exchange material or an organic extractant-containing solvent (for cesium and strontium removal) or 2) solvents for selective separation of TRU elements (e.g., TRUEX process). These coatings, by their chemical nature, selectively separate the contaminants onto the particles, which can then be recovered from the tank using a magnet. Once the particles are removed, the contaminants can either be left on the loaded particles and added to the glass feed slurry or stripped into a small volume of solution so that the extracting particles can be reused. The status of the chemistry and separation process is discussed in this paper.     

Evaluation of Thermodynamic Parameters for Separation of Hexavalent Chromium by Fly Ash

Abstract

Kinetics and thermodynamic parameters of Cr⁶⁺ separation by fly ash from aqueous solution has been evaluated. It was found that the separation process is partly diffusion controlled and endothermic in nature. The mass transfer coefficient increases with an increase in temperature. The activation energy and change of enthalpy were also evaluated and found to be 17.5 kJ/mol and 14.47 kcal/mol, respectively. The free energy of the process was small but positive, and it decreases with an increase of temperature. The change of entropy was found to be small and remains unchanged over the 30 to 50°C temperature range. This process follows the Langmuir isotherm model where Q _o and b were also determined at different temperatures.     

Dielectrophoretic Gold Particle Separation

Abstract

We present a novel process for gold particle separation from aqueous setup with a high separation efficiency and without any environmental risk. Dielectrophoresis (DEP), as the main mechanism of this separation process, is applied for the first time to separate gold even continuously from a raw mineral mixture. Electrothermal and high-pass-filter effects, occurring in DEP with water as liquid phase, were investigated and considered during the design of the separation process. The experimental results demonstrate that even ultra thin gold particles can be separated from a raw mineral mixture with an efficiency of up to 88% at an electric field of 32 kV/m and 200 kHz in continuous operation with specific fluid flow of about 400 m³/(m h).     

Hydrophobic Flocculation Flotation for Beneficiating Fine Coal and Minerals

ABSTRACT

It is shown that hydrophobic flocculation flotation (HFF) is an effective process to treat finely ground ores and slimes so as to concentrate coal and mineral values at a fine size range. The process is based on first dispersing the fine particles suspension, followed by flocculation of fine mineral values or coal in the form of hydrophobic surfaces either induced by specifically adsorbed surfactants or from nature at the conditioning of the slurry with the shear field of sufficient magnitude. The flocculation is intensified by the addition of a small amount of nonpolar oil. Finely ground coals, ilmenite slimes, and gold finely disseminated in a slag have been treated by this process. Results are presented indicating that cleaned coal with low ash and sulfur remaining and high Btu recovery can be obtained, and the refractory ores of ilmenite slimes and fine gold-bearing slag can be reasonably concentrated, leading to better beneficiation results than other separation techniques. In addition, the main operating parameters affecting the HFF process are discussed.     

A Comparison of Static Bed and Moving Bed Chromatography

Abstract

An analysis of static and moving bed perfect column chromatography is carried out for the separation of a binary mixture having constant separation factor isotherms. It is shown that the carrier requirements are identical for both methods of operation. The model does not provide information on the length of the moving bed column, but shows that the length of the static bed column can be made vanishingly small by reducing the duration of feed intervals. Furthermore, separating the feed bands only partially can - lead to a substantial reduction in the length of the static column at fixed separation rates.     

A Calculation Procedure for Designing Ideal Centrifugal Separation Cascades

Abstract

A numerical method is presented for determining flow rates in centrifugal isotope separation cascades that satisfy the required “ideal cascade” conditions. This method is an iterative method, which in the iteration process uses the q-iteration method to give the concentration and distributions of components under a specified hydraulic status for a cascade; and then, based on the concentration distributions, solves the algebraic equations describing the hydraulic status of the cascade to improve the specified hydraulic status towards the required “ideal cascade” conditions. The material losses in the cascade pipes and centrifuges are taken into account. Numerical simulations are performed by taking an MARC cascade with variant stage separation factors as an example. The results from four cases with and without material losses are compared. The results demonstrate that the method works very well, and show that when the material losses are nonexistent or very small, the concentration distributions can exactly satisfy the “ideal cascade” condition; but when the material losses are large, the “ideal cascade” condition can not be satisfied, but the method can produce a solution that allows the condition to be approximately satisfied.     

Ion-Expulsion Ultrafiltration to Remove Chromate from Wastewater

Abstract

In ion-expulsion ultrafiltration, a water-soluble colloid with the same charge as the target ion to be removed is added to water. This stream is then treated by ultrafiltration with membrane pores small enough to reject the colloid. In this study, chromate was removed from water using polystyrene sulfonate as the colloid in both batch-stirred cell and spiral-wound ultrafiltration devices. At very low pressures, Donnan equilibrium could be used to describe the permeate chromate concentration. As the pressure increased, diffusional effects caused the separation to become poorer. A spiral-wound unit resulted in a much higher separation efficiency than a stirred cell in this process.     

Sonic Dewatering of Large Particle Dispersions

Abstract

A new phenomenon has been discovered wherein separation of liquids from large particle dispersions can be accomplished with ultrasound. In our experiments, sonic capillary-wave action produced small droplets of water ejected using about 10% of the energy needed to thermally vaporize the water. In order for the separation to occur, the solid particle diameter must be greater than the droplet size, which can be predicted by Lang's formula. The solid particles remain behind as a disintegrable clump bound by occluded liquid.     

Floe Foam Flotation of Chromium(VI) with Polyelectrolytes

Abstract

The separation efficiency of the floe foam flotation of chromium(VI) with Fe(II) from aqueous solutions with high ionic strength can be improved by adding a very small amount of polyelectrolyte (either cationic or anionic polymer) as an activator. The possible mechanisms by which flotation is affected by polyelectrolytes are discussed. The effects of the order of the addition of the reagents (polyelectrolyte and base) on flotation and sedimentation are also studied. It was found that effective separation of chromium(VI) by floe foam flotation with Fe(II) can be achieved for a rather wide range of initial chromium(VI) levels by using the same treatment parameters.     

Fractionated Vacuum Swing Adsorption Process for Air Separation

Abstract

A novel adsorptive process for air separation using a zeolitic adsorbent is described. The process essentially consists of three simple cyclic steps, and it can be used for simultaneous production of an 80—90% oxygen-enriched gas and a 98 + % nitrogen-enriched gas from ambient air. Successful operation of the process requires the use of a zeolite which exhibits high nitrogen adsorption capacity and selectivity from air. The role of nitrogen adsorption selectivity of the zeolite in the vacuum desorption process is examined, and experimental performance data for the air separation process are reported.     

Separation performance of an 8 mm mini-hydrocyclone and its application to the treatment of rice starch wastewater

ABSTRACT

The rice starch particles are difficult to separate from starch suspensions for its fine diameter. In this work, an 8 mm mini-hydrocyclone is designed, and its separation performance and potential for the treatment of rice starch wastewater is investigated. The capacities, total separation efficiencies of an 8 mm mini-hydrocyclone and a 10 mm mini-hydrocyclone are compared. The experimental results reveal that the total separation efficiency of the 8 mm mini-hydrocyclone is approximately 13% higher than that of the 10 mm mini-hydrocyclone. A total separation efficiency of 92.1% was obtained using a two-stage hydrocyclone separation process comprising two 8 mm mini-hydrocyclones connected in series. The research findings can be utilized to efficiently treat the rice starch wastewater.     

Diffusion Transport Vector for Multicomponent Gas Separation in Ultracentrifuge

Abstract

Simplified diffusion transport vector expressions for multicomponent gas mixture mass transfer analysis have been derived. Approximate relations for the general diffusion coefficients for multicomponent gas separation in an ultracentrifuge for both isotope and nonisotope mixtures are developed. Taking into account that diffusion coefficients matrices are diagonally dominant, a simple relationship for diffusion transport vectors for the case of isotope separation is derived. It is shown that the relative inaccuracies in separative power and separation factors calculation are less than 1-2%. Analogous relationships for diffusion coefficients for the separation of a nonisotope mixture containing small admixtures in the main gas are suggested. These relationships can be used when the total mole fraction of the admixtures is less than 5%.     

Process Modeling of Laser Photochemical Reactor

Abstract

The applicability of conventional process engineering terms like value function, separative work unit, etc. to the laser isotope separation process has been established through appropriate formulation of the problem. The value function developed in this paper has been shown to be useful in arriving at guidelines for optimal design and operation of an isotope separation plant. A direct and simple model has been developed for a single-phase single-component laser photoreactor stage. This model, incorporating the key features and constraints of the laser isotope separation process, can provide an analysis and design basis to the process engineer.     

A Study on Triple-Membrane-Separator (TMS) Process to Treat Aqueous Effluents Containing Uranium

Abstract

An effective process incorporated with the novel membrane separation technology was developed to recover uranium from the filtrate effluent of uranium dioxide conversion processes. The prominent feature of the process is that it utilizes separation characteristics of three different types of membranes as follow: separation of uranium species from effluent of high fluoride content by ultrafiltration membrane, separation of uranium species from effluent of low fluoride content by reverse osmosis membrane, precipitation of uranium species with hydrogen peroxide, and filtration of uranium bearing precipitates by microfiltration membrane. The process is simple and feasible for treatment of liquid waste containing both soluble and suspended uranium species. The recovery of uranium can achieve 95% and the treated effluents meet the current environmental standards.     

Opportunities for Membrane Technologies in the Treatment of Mining and Mineral Process Streams and Effluents∗

Abstract

The membrane separation technologies of microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are suitable for treating many dilute streams and effluents generated in mining and mineral processing. Membrane technologies are capable of treating these dilute streams in order to produce clean permeate water for recycle and a concentrate that can potentially be used for valuable metals recovery. Membrane technologies can be utilized alone, or in combination with other techniques as a polishing step, in these separation processes. A review of potential applications of membranes for the treatment of different process streams and effluents for water recycling and pollution control is given here. Although membranes may not be optimum in all applications, these technologies are recognized in the mining sector for the many potential advantages they can provide.

     

SEPARATION OF IONIC SPECIES UNDER SUPERCRITICAL WATER CONDITIONS

ABSTRACT

The unique characteristics of supercritical water (SCW) offer potentially attractive processing options that can be explored for reaction and separation purposes. While supercritical water oxidation (SCWO) can achieve high organic conversion efficiencies, low and relative solubilities of inorganic species in SCW may be further utilized for in situ separation of potential by-products from the SCWO process effluent.

This paper describes a novel method for separating ionic species under SCW conditions. The concept is based on relative solubilities of different ionic species in SCW. Laboratory-scale demonstration tests were conducted with a Nylon monomer manufacturing process wastewater containing sodium hydroxide, sodium borate, carboxylic acids, and water. The process achieved (1) effective destruction (>99%) of organic components in the wastewater; (2) selective precipitation of sodium (>99.5%) as carbonates produced from oxidation of the organic components; and (3) efficient recovery of boron (>90%) as boric acid in the reactor effluent. The sodium removal efficiency is governed by the solubilities of sodium carbonates in SCW and, therefore, can be directly improved by increasing process temperature. As a result of the temperature increase, both organic destruction and boron recovery efficiencies may be enhanced.

This method of selective separation of ionic species in SCW has potential for a wide range of processing applications.     

A Mathematical Analysis of Membrane Separation Parameters for Liquid/Liquid Dialysis in Single or Multiple Stages

Abstract

The effects of membrane separation parameters using liquid/liquid dialysis under idealized conditions and using hollow fiber geometry were calculated with the aid of a computer. These calculations were carried out for both single stage and multiple stages. Membrane separation parameters include the intrinsic properties of the membrane, the nature of the dialysis solvents, the flow rates of both feed and solvent streams, and the dimension of the hollow fiber. It was concluded that an efficient process using liquid/liquid dialysis requires a membrane with a high intrinsic permeability constant and a reasonable separation factor, as small an inner radius of hollow fiber as is practical, and a dialysis solvent with an acceptable activity coefficient for the key species and a flow rate suitably coupled to that of the feed.     

Foam Fractionation and Precipitate Flotation of Zinc(II)

Abstract

The hydrolytic behavior of a metal can be related to its removal by foaming. In this study the effect of pH and ionic strength on the foam separation of 0.1 mM zinc (II) was investigated using different concentrations of sodium lauryl sulfate as the collector. At low pH Zn²⁺ ion was removed by foam fractionation while above pH 8 Zn(OH)²(s) was removed by precipitate flotation. The results demonstrate that precipitate flotation is a more efficient removal process than the foam separation of soluble metal species.     

Continuous Separation in Split-Flow Thin (SPLITT) Cells: Potential Applications to Biological Materials

Abstract

We recently described a broad class of techniques in which separation is achieved over a submillimeter path extending along the thin dimension of a special separation cell termed a SPLITT cell. The separation is converted into a continuous process by flow through the cell, and the products are collected with the aid of flow splitters. The separation is rapid and predictable by virtue of the simple geometry of the cell. Separation can be based on differences in sedimentation coefficients, densities, electrophoretic mobilities, isoelectric points, diffusion coefficients, etc., depending on operating details. We describe here the principles of SPLITT cells and summarize our preliminary laboratory findings. We discuss various approaches for utilizing the SPLITT system to separate biological materials with components spanning the mass range from the extremes of biological cells down to that of simple amino acids.     

The Influence of Entrainment on Distribution Ratios in Complexation Studies

ABSTRACT

Entrainment of a small amount of one phase in the other after phase separation is almost impossible to avoid in solvent extraction. The effect on distribution ratios, D-values, is that the measurement at high D-values results in lower values than the true D-value. The opposite happens with the aqueous phase. Entrainment reduces the maximum effective separation of two substances using countercurrent solvent extraction in mixer-settlers, pulsed columns, and centrifugal extractors. When solvent extraction is used to study the complex formation, the entrainment of a small amount of the organic phase in the aqueous phase reduces the limiting slope observed at low D-values and sometimes makes the accurate determination of one or more of the stability constants impossible.

On the other hand, the reduction of the expected limiting slope yields a tool for estimation of the entrainment in the specific case and hence makes it possible to get entrainment data that can be used in comparisons of the efficiencies of different phase separation techniques and equipment.

In this work, the effect of entrainment on “effective” D-values is derived in a quantitative way, yielding equations that can be either used to predict “effective” D-values from any given relative entrainment in any phase or used to estimate entrainment by comparing measured “effective” D-values and the corresponding data from test tube experiments with no entrainment.