Timothy N. Hunter

University of Leeds · School of Chemical and Process Engineering

Two graphene oxide (GO) materials were characterised and their performance as adsorbents for common ionic dyes was investigated. The GOs were demonstrated to possess significantly different flake sizes; here termed Smaller Flake GO (SFGO) and Larger Flake GO (LFGO). Kinetics and isotherm studies using both cationic Methylene Blue (MB) and anionic M...

Inorganic/organic composite nuclear wastes have poor settling properties which hinder major UK decommissioning operations. Improving the settling properties of these wastes and the accurate prediction of settling rates is therefore key. However, constricted access and limited monitoring capability in radioactive environments limits the use of prima...

This study investigates the settling behaviour of bidisperse colloidal silica suspensions in two different size ratios (100:500 nm and 500:800 nm) with various mixture ratios and volume fractions, using an analytical photocentrifuge. For dilute systems, translation of settling rate profiles to size distributions resulted in more accurate measuremen...

The research develops a simplified heat transfer model that allows prediction of the temperature response of the radioactive contents of the buffer storage tank at Sellafield. The model emanates from an energy balance around a singular tank with comprehensive analysis of the heat transfer phenomena. A converged solution has been demonstrated by com...

This study investigates the dynamics of a novel, oscillatory, intensified plug-flow reactor – an agitated tubular reactor (ATR) – designed for efficient flow processing of solid-liquid mixtures. The relative movement of the reactor and agitator bar, and associated effects on fluid mixing were characterised physically with a suite of experimental in...

TRANSCEND (Transformative Science and Engineering for Nuclear Decommissioning) is a collaborative research consortium comprising 11 universities and 8 industry partners. The £9.4 million research program, funded primarily by the Engineering and Physical Sciences (EPSRC) Research Council of the UK, incorporates >40 projects in total, which will addr...

Water is a valuable resource that is needed to sustain life, but is also essential in many engineering processes, which unavoidably leads to large volumes of water being contaminated. To achieve safe discharge and also recover valuable “pollutants”, better performing sorbents are needed to rapidly and efficiently decontaminate water and generate mi...

In wet stirred milling of Al-doped TiO2, sodium hexametaphosphate (SHMP) is used as a small molecule dispersant to improve milling performance. In both acidic and basic conditions, SHMP interacts strongly with Al-doped TiO2 and remains stable during milling. Considering the apparent and true particle breakage performance, at pH 10.3, the optimal do...

No PDF available ABSTRACT Complex magnox ponds at Sellafield retain hydroxide-based sludge with unknown physicochemical properties. The sludge is a corroded form of magnesium-based fuel cladding used in first generation magnox reactors. Long term storage and open-air aqueous conditions are major contributors to corrosion. Waste needs to be transpor...

This paper reports on use of a commercial ultrasonic velocity profiler (UVP) to monitor changes in concentration within complex suspensions. A calcium carbonate (CaCO3) nuclear waste simulant was used with a high molecular weight anionic polymer flocculant to produce varying suspension environments. 2 MHz ultrasonic transducers were used in both in...

In this study, an acoustic backscatter system was used with single broadband transducers utilising narrowband excitation at multiple frequencies of 2.00, 2.25 and 2.50 MHz, to determine the scattering properties of three sizes of glass particles (40, 78 and 212 µm) in liquid suspensions. A calibration procedure was developed to initially measure th...

The aim of this study was to understand the efficacy of widely available minerals as dual-function adsorbers and weighter materials, for the removal of toxic azo-type textile dyes when combined with coprecipitation processes. Specifically, the adsorption of an anionic direct dye was measured on various mineral types with and without the secondary c...

Mg(OH)2 suspensions were floated utilising sodium dodecyl sulphate (SDS) and sodium lauroyl isethionate (SLI) collectors, for rapid dewatering of radwaste suspensions. Freundlich adsorption isotherms were first used to compare the adsorption densities of SDS and SLI on Mg(OH)2 surfaces, to determine the maximum monolayer coverage capacity, and were...

A comparison of polymeric flocculation aids for the dewatering of metal hydroxide based legacy waste suspensions was carried out. Traditional vendor bought; long chain polymer flocculants utilising "bridging" flocculation mechanisms were compared to a lab synthesised amphiphilic diblock copolymer, which utilised a "charge patch" flocculation mechan...

Natural clinoptilolite was studied to assess its performance in removing caesium and strontium ions, using both static columns and an agitated tube reactor (ATR) for process intensification. Kinetic breakthrough curves were fitted using the Thomas and Modified Dose Response (MDR) models. In the static columns, the clinoptilolite adsorption capacity...

The stirred wet milling of aluminum-doped TiO2 was considered. At milling speeds of 2500–6000 rpm, the pHi.e.p. shifted from pH 5.7 to pH ~8, while at 8000 rpm the shift in pHi.e.p. was smaller. Milling at 8000 rpm, the reduced milling performance was attributed to a change in the predominant milling mechanism. XPS revealed an approximate linear co...

Complex magnox ponds at Sellafield retain hydroxide-based sludge with unknown physicochemical properties where the sludge is a corroded form of magnesium-based fuel cladding. Long term storage and open-air aqueous conditions have been major contributors to corrosion and now the waste requires transportation to interim storage using engineered pipel...

Light scattering is a fundamental property that can be exploited to create essential devices such as particle analysers. The most common particle size analyser relies on measuring the angle-dependent diffracted light from a sample illuminated by a laser beam. Compared to other non-light-based counterparts, such a laser diffraction scheme offers pre...

In this study, magnesium hydroxide (Mg(OH)2) suspensions were flocculated using two polyacrylamide-poly(acrylic acid) copolymers with charge densities of 30% or 40%. Structural characteristics, including particle size distribution, shape and fractal dimension of the resultant flocs were investigated using complementary techniques; static light scat...

Recent advances in the latest generation of MEMS (micro-electro-mechanical system) Fabry-Pérot interferometers (FPI) for near infrared (NIR) wavelengths has led to the development of ultra-fast and low cost NIR sensors with potential to be used by the process industry. One of these miniaturised sensors operating from 1350 to 1650 nm, was integrated...

This paper reports application of ABS (Acoustic Backscatter Systems) to address nuclear waste management within the UK. ABS offers a route towards an online monitoring system to characterise wastes safely and remotely in real-time, during pipeline transportation; resulting in reduced hazard reduction timescales and taxpayer cost savings. Here, an u...

Flotation using cationic surfactants has been investigated as a rapid separation technique to dewater clinoptilolite ion exchange resins, for the decontamination of radioactive cesium ions (Cs⁺) from nuclear waste effluent. Initial kinetic and equilibrium adsorption studies of cesium, suggested the large surface area to volume ratio of the fine zeo...

A facile and low-cost fabrication route, inspired by the adhesive proteins secreted by mussels, has been developed to prepare a clay-based composite hydrogel (DHG(Cu)) containing hexacyanoferrate (HCF) nanoparticles for the selective removal of Cs+ from contaminated water. Initially, montmorillonite was exfoliated prior to coating with a thin layer...

Research and development related to the processing of recycled materials has grown progressively in recent times, as scientists endeavour to integrate sustainability criteria, depletion of natural resources, reducing the energy of technological processes involving extraction and processing of raw materials, etc. When it comes to processing slate, i...

The rheology of non‐Newtonian slurries are measured in a recirculating pipe loop using an acoustic velocimetry‐pressure drop technique at very low flow rates and variable solids loadings. The technique avoids (a) settling at low solids concentration, a shortcoming of bench rheometry, by using a vertical test section, and (b) physical sampling, prov...

PurposeThe current trend for continuous drug product manufacturing requires new, affordable process analytical techniques (PAT) to ensure control of processing. This work evaluates whether property models based on spectral data from recent Fabry–Pérot Interferometer based NIR sensors can generate a high-resolution moisture signal suitable for proce...

The use of zeolites as ion-exchange resins, such as clinoptilolite, are common in the industrial and mining effluent treatment of heavy metals. However, while fine powdered material is more efficient, most processes still employ low-flow elution columns and large resins, as there are significant issues with fine particulate separation using gravita...

This paper presents an overview into the use of acoustic backscatter systems (ABS) for the in situ characterization of nuclear waste sludge concentration, size and aggregation, highlighting key achievements from the University of Leeds. Previous projects funded through the Engineering and Physical Sciences Research Council (EPSRC) UK and Innovate U...

Flotation has been effectively demonstrated as a low footprint, high efficiency separation process when utilising simple anionic surface modifying agents such as sodium dodecyl sulphate (SDS). These agents increase hydrophobicity to remove suspended cationic surface charged particulates such as Mg(OH)2 from waste suspensions similar to those at Bri...

The performance of a pilot-scale horizontal sedimentation tank was characterised utilising computational fluid dynamics (CFD) and a bespoke ultrasonic backscatter array, for both spherical glass and flocculated calcite separation. The CFD simulation was developed in OpenFOAM, using algebraic slip and hindered settling models, in order to solve the...

The minerals calcium carbonate and talc were filtered under various conditions of filtrate flow rate and suspension concentration, using constant rate conditions with the aid of a peristaltic pump to draw the filtrate. Cake concentrations of between 0.41 and 0.53 v/v for calcium carbonate and 0.19 and 0.26 v/v for talc were recorded. The mean sizes...

The critical deposition velocity in horizontal pipe flow of liquid-solid slurries separates bed-forming and fully suspended flows. A compilation of critical deposition velocity data is presented using new experimental data (for particles ranging from 9 to 690 µm in diameter) along with data from the literature, and a close correlation between the p...

Soft sediments exhibit complex and varied deformation behavior during in situ bubble growth, however the sediment microstructure is often neglected when predicting bubble networking or fracture propagation dynamics. This study considers three chemically similar Mg(OH)2-rich sediments, which differ slightly in their particle size distributions and m...

Natural clinoptilolite, of relatively low-grade, was investigated for its capability to remove cesium and strontium ions from water and simulated seawater. To improve its capacity, the material was pre-activated with concentrated NaCl and HCl solutions. Additionally, it was milled to a number of < 300 μm size fractions, to expose exchange sites. El...

This paper investigates the characterisation of alumina-doped titania nanoparticles, milled under high-shear over time, in the presence of sodium hexametaphosphate (SHMP) dispersant. Transmission electron microscopy (TEM) indicated that prolonged milling times led to the formation of 10 nm particle fines which were electrostatically attracted to la...

The resonance properties, frequency and half-band-half-width, of a quartz crystal microbalance (QCM) immersed in concentrated suspensions of 16.2 vol% TiO 2 are shown to be a function of pH. The overall QCM response is dependent on the complex interactions between the QCM sensor and overlying particle suspension. Atomic force microscopy confirms pH...

To aid in the transportation, dewatering and storage of radioactive UK legacy waste sludges at Sellafield Ltd., the application of an Acoustic Backscatter System (ABS) was investigated in this study, as a method for monitoring suspended solids concentration and consolidation of cohesive and aggregated sludges (that form the basis of many wastes at...

Based on the nuclear industry in the U.K., storage of nuclear waste poses a particularly complex challenge. Specifically, this research is concerned with post-PUREX (Plutonium Uranium Redox EXtraction) high level waste, known as HAL (Highly Active Liquor), containing nitric acid and a host of fission products. HAL is concentrated, and stored in HAS...

Sodium Carboxymethyl Cellulose (Na CMC) is used for its thickening and swelling properties in a wide range of complex formulated products for pharmaceutical, food, home and personal care applications, as well as in paper, water treatment and mineral processing industries. To design Na CMC solutions for applications, a detailed understanding of the...

As a low footprint, high efficiency separation process, Dissolved Air Floatation (DAF) could effectively be retrofitted into existing waste management facilities at nuclear sites such Sellafield and Hanford to rapidly separate particulates from aqueous suspensions. The simplicity (no moving parts) and size of this technology coupled with low cost o...

The scattering and attenuation of megahertz frequency acoustic backscatter in liquid suspensions, is examined for a range of fine organic and inorganic particles in the Rayleigh regime, 10−4 < ka < 100 (where k is the wavenumber and a the particle radius) which are widely industrially relevant, but with limited existing data. In particular, colloid...

The complexity associated with droplets spreading on surfaces has attracted significant interest for several decades. Sustained activity results from the many natural and manufactured systems that are reliant on droplet-substrate interactions and spreading. Interfacial shear rheology and its influence on the dynamics of droplet spreading has to dat...

This study investigated dispersions analogous to highly active nuclear waste, formed from the reprocessing of Spent Nuclear Fuel (SNF). Non-radioactive simulants of spheroidal caesium phosphomolybdate (CPM) and cuboidal zirconium molybdate (ZM-a) were successfully synthesised; confirmed via Scanning Electron Microscopy (SEM), powder X-ray diffracti...

The ongoing boom of industrialization is conflicted by concerns regarding increased levels of environmental contamination, in particular the uncontrolled release of heavy metal ions and radionuclides into soils and groundwater systems. The extent of contamination can be substantial, hence ways to remediate and reduce the volume of waste for further...

In this study, diblock copolymers poly(methyl methacrylate) - block - poly(2-dimethylaminoethyl methacrylate) (pMMA-b-pDMAEMA) are investigated for the steric stabilization of latex particles and the subsequent use of these latex particles as Pickering emulsifiers. Solution properties of the diblock copolymers highlight that the pDMAEMA block lengt...

Many consolidated sediments experience in situ gas generation from methanogenesis, corrosion or radiolysis reactions and can retain bubbles for long periods. Particular interest is motivated by the retention and acute release of flammable hydrogen from nuclear legacy waste sludge. X‐ray computed tomography was employed to observe 0.07‐10 mm bubble...

This paper demonstrates the influence of surface charge chemistry on the application of nuclear magnetic relaxation measurements (NMR relaxometry) for the in situ determination of particle surface area, in the presence of high electrolyte concentration. Specifically, dispersions of titania, calcite and silica with and without 1 M KCl were investiga...

Understanding the sedimentation behaviour of colloidal suspensions is crucial in determining their stability. Since sedimentation rates are often very slow, centrifugation is used to expedite sedimentation experiments. The effect of centrifugal acceleration on sedimentation behaviour is not fully understood. Furthermore, in sedimentation models, in...

The application of quartz crystal microbalance (QCM) as a device to measure the rheology of colloidal suspensions has been studied. Using a commercial dip-probe QCM, the yield stress of magnesium hydroxide suspensions has been correlated to the resonance properties of a 5 MHz AT-cut quartz sensor. A stable resonance baseline was first established i...

This study investigated the complex settling behaviour of colloidal particles with varied surface charge and shape factors, of specific relevance to nuclear waste processing. Caesium phosphomolybdate (CPM), zirconium molybdate (ZM) and zirconium citromolybdate (ZMCA) were firstly synthesised, producing spheroidal, cubic and rectangular cuboidal mor...

Acoustic backscatter systems offer a flexible technique to measure dispersion concentration and particle size, via inversion of the return echo voltage response of pulse-echo signals in the MHz range. While there have been recent developments in how backscatter models can be broadened in marine applications there is little data available for the Ra...

Acoustic backscatter systems offer a flexible technique to measure dispersion concentration and particle size, through inversion of the return echo voltage response of pulse-echo signals in the MHz range. This study explores the use of the ultrasound array research platform to measure the suspended particle attenuation constant using acoustic backs...

The selective capture of mobile radioactive nuclides, such as 137Cs+, is crucial to the clean-up and remediation of contaminated environments. While remediation remains a challenging task, the current study considers novel organo-clay composites containing potassium copper hexacyanoferrate (KCuHCF) as a viable option for large-scale clean-up. A thr...

Retention of hydrogen bubbles within consolidated soft sediments represents an important safety consideration for the management of legacy nuclear wastes due to the potential for acute gas release. Gas retention sufficiently reduced the bulk density of intermediate yield stress (< 800 Pa) sediments for the bed to become buoyant with respect to an a...

Measurements of time-dependent bedforms produced by the deposition of solid plastic particles in two-phase liquid-solid flows were performed using a novel ultrasonic echo method and via video image analysis in a 100-liter, closed-pipe slurry flow loop. Results are presented for the settled bed thicknesses over a range of nominal flow rates and init...

Impinging jets are utilized in numerous applications, including nuclear waste treatment, for both the erosion of sediment beds and maintaining particulates in suspension. Pulse-echo ultrasonic methods offer great potential for the in situ monitoring of critical mixing and settling dynamics, in concentrated dispersions. A non-active scaled version o...

In water treatment the flocculation of particles into larger aggregates or ‘flocs’ allows impurities or solid material to be removed more easily by sedimentation. One example is where soluble phosphorus is removed by dosing with ferric sulphate to form a precipitate containing the phosphorus. Dosing usually requires rapid mixing of the ferric sulph...

Acoustic backscatter systems are an ultrasonic technique normally utilised for characterising particle size and concentration in large, dilute sediment suspensions. This book outlines their novel application for the in situ characterisation of concentrated dispersions of many arbitrary particles, including those in the colloidal size range. An alte...

Real time in situ characterisation of solids concentration would aid operational understanding and improve efficiency in many industrial systems. This is especially true in the processing of legacy nuclear wastes where hazardous material is encountered. Acoustic methods have been previously demonstrated for the measurement of concentration in solid...