Abhishek Biswas

Leaching of pure and cobalt bearing goethites in sulphurous acid: kinetics and mechanisms

Abstract The initial kinetics of sulphurous acid leaching of well characterised synthetic pure goethite (G–O) and goethites containing cobalt in sorption [GCo(S)] and co-precipitation [GCo(C)] modes have been studied. The interfacial reaction controlled nature of iron dissolution from different samples is indicated by the activation energy of about 65 kJ/mol. The rates of iron and cobalt dissolution from different samples showed a stronger dependence on the concentration of SO2(aq.) compared with other solution species such as HSO3− and H+. The particles were found to be non-uniformly attacked, preferentially on multi-domain grain boundaries. The results of infra-red (IR) spectroscopy on leach liquors indicated that SO42− is the major species formed during leaching. The half order of dependence of the iron dissolution rate on the concentration of SO2(aq.) was corroborated by theoretical analysis of the electrochemical leaching reaction by the Butler-Volmer equation. It is proposed that chemically controlled leaching of cobalt (Ea≈82 kJ/mol) from GCo(S) may involve the reaction of two molecules of SO2(aq.) with one molecule of surface Co(OH)2 species. Cobalt and iron dissolve from GCo(C) congruently; the dissolution is controlled by the structure and leachability of the host goethite phase.

Physico-chemical nature and leaching behaviour of goethites containing Ni, Co and Cu in the sorption and coprecipitation mode

Abstract Goethite (α-FeOOH) samples containing Ni, Co and Cu in coprecipitation and sorption mode were synthesized and characterized in terms of chemical composition, surface area, phase constituents, crystallinity and structural disorder (by XRD) and crystal size and morphology (by TEM). Dissolution behaviour of Fe in Ni-, Co- and Cu-bearing goethite samples in sulfuric and sulfurous acid leaching systems have been compared with the behaviour of a pure goethite sample and correlated with the physical characteristics of the samples. Minor elements interfere with the dissolution of iron in sulfurous acid leaching. Elements in the sorption mode are easily leachable compared to the coprecipitation mode. In the latter case these may be present as a part of the goethite structure or as occluded oxyhydroxide. The implications of these results are discussed for acid leaching of manganese nodules.

Zinc recovery from zawar ancient siliceous slag

Abstract Zinc is found to exist in Zawar ancient slag in India mainly as the silicate phases hemimorphile, Zn 4 (OH) 2 Si 2 O 7 ·H 2 O, and willimite, Zn 2 SiO 4 , and also as the hydrozycarbonate phase hydrozincite, Zn 5 (CO 3 ) 2 (OH) 6 . Various processing techniques show that the non-silicate mineral can be easily leached by acid. Willemite and the hemimorphite phase can also be leached by acid. However, zinc recovery apparently is poor; this phenomenon has been ascribed to chelation or adsorption of Zn 2+ by colloidal/polymeric silicic acid. Neutralisation, coagulation and precipitation of silicic acid by Al 3+ ions distinctly improve zinc recovery. The “fast leaching” technique, which makes use of the water-starved nature of the silicate—acid system shows distinct promise. Recovery of zinc of more than 80% is reported.

Design and development of a low-cost biphasic charge-balanced functional electric stimulator and its clinical validation.

Functional electric stimulators that produce near-ideal, charge-balanced biphasic stimulation waveforms with interphase delay are considered safer and more efficacious than conventional stimulators. An indigenously designed, low-cost, portable FES device named InStim is developed. It features a charge-balanced biphasic single channel. The authors present the complete design, mathematical analysis of the circuit and the clinical evaluation of the device. The developed circuit was tested on stroke patients affected by foot drop problems. It was tested both under laboratory conditions and in clinical settings. The key building blocks of this circuit are low dropout regulators, a DC-DC voltage booster and a single high-power current source OP-Amp with current-limiting capabilities. This allows the device to deliver high-voltage, constant current, biphasic pulses without the use of a bulky step-up transformer. The advantages of the proposed design over the currently existing devices include improved safety features (zero DC current, current-limiting mechanism and safe pulses), waveform morphology that causes less muscle fatigue, cost-effectiveness and compact power-efficient circuit design with minimal components. The device is also capable of producing appropriate ankle dorsiflexion in patients having foot drop problems of various Medical Research Council scale grades.

Effect of FES in rehabilitation of cerebral palsy children by analysis of surface EMG in tibialis anterior muscle

In this study we have evaluated the efficacy of Functional Electrical Stimulation (FES) in the rehabilitation of spastic Cerebral Palsy (CP) children, by surface electromyographic (sEMG) analysis of the Tibialis Anterior (TA) muscles. Ten children with spastic diaplegic/hemiplegic cerebral palsy within the age group of 5 to 14 years received both FES for 30 minutes and the conventional physiotherapy for 30 minutes a day, for 5 days a week, up to 12 weeks. The measurement of electromyography (EMG) of both the baseline (at the initiation) and post treatment (after intervention) were obtained. These data were analysed for both amplitude and frequency related parameters. The results report a rise in Root Mean Square (RMS), Mean Absolute Value (MAV), EMG peak amplitude and Integrated EMG (IEMG) values. Improvement was also seen in Median Frequency (MDF), Mean Frequency (MNF) and the total power of the EMG power spectrum. Hence we can conclude that FES combined with conventional physiotherapy improves the muscle strength in spastic CP children.

Characterization of synthesized wolframite minerals and their leach residues

The physical properties and benefication potential of wolframite (FexMn1−x)WO4 have been shown to depend heavily upon x or the FeMn ratio. A series of wolframites with x varying between zero and one have been synthesized and lattice parameters determined. Alkali-leaching of ferberite (FeWO4) has been found to be topotactic, with selective removal of tungsten and production of a high FeW ratio on the surface. The replacement of iron with manganese in the wolframite structure seems to result in a less compact lattice and faster and less selective dissolution.

Modelling a BCI system to estimate FES stimulation intensity for individual stroke survivors in foot drop cases

This work provides a model to estimate stimulation level required for hemiplegic patient to achieve foot dorsiflexion using BCI approach. The model’s input is EEG from motor cortex of hemiplegic patient. The model’s output is estimation of stimulation strength. The delta mean and alpha peak frequencies are found to be suitable as EEG features to establish the relationship between EEG parameters and stimulus strength for this model. This model is self-adaptive in nature. As therapeutic procedure continues, the model uses a feedback loop, so that it can fine tune the stimulus strength to optimum value for individual patients. The model is prepared by using analysis of EEG feature from all the frequency bands and stimulus strength as observed clinically in 15 stroke patients while achieving dorsiflexion.

Comparison of Gait Parameters and Locomotor Capability Index in Transtibial Amputee using Two Different Types of Suspension System

Background: The main purpose of all suspension systems is prosthesis retention. Numerous means to suspend below-knee (BK) prostheses have been developed. Although suspension systems generally used for BK prostheses have similar functions, choices for prescription are not totally clear. Patellar tendon bearing (PTB) suspension principles are effective with many patients; however, those with short limbs may not achieve complication-free suspension. The fact that variations of BK suspensions continue to appear suggests that a universal suspension system is not yet available. Objective: To find out the effect of two types of suspension system on gait parameters and locomotor capabilities index in subject with unilateral transtibial amputee. Study design: Single study with post experimental design. Methods and measures: Two different suspension systems such as supracondylar and cuff suspension for below knee prostheses were tested on 30 adults with unilateral transtibial amputees. All subjects walked with prosthesis. Data regarding gait parameters and Locomotor capabilities index were measured. Gait parameters such as velocity, cadence, step length, stride length were evaluated by CDG gait analyser and walking abilities of the subjects were evaluated by locomotor capabilities index (LCI). Result: The results revealed that the statistical difference between two suspension systems is significant (p<0.05). Study suggested that using supracondylar suspension velocity, cadence, stride length and step length increased compared to cuff suspension. But value of Locomotor capability index was more in cuff suspension compared to supracondylar suspension which indicates use of cuff suspension reduces fear of falling and patients feels more secure. Conclusion: The findings of the study thus support the hypothesis that there were significant difference with different suspension systems on gait parameters and locomotor capabilities index.Background: The main purpose of all suspension systems is prosthesis retention. Numerous means to suspend below-knee (BK) prostheses have been developed. Although suspension systems generally used for BK prostheses have similar functions, choices for prescription are not totally clear. Patellar tendon bearing (PTB) suspension principles are effective with many patients; however, those with short limbs may not achieve complication-free suspension. The fact that variations of BK suspensions continue to appear suggests that a universal suspension system is not yet available.Objective: To find out the effect of two types of suspension system on gait parameters and locomotor capabilities index in subject with unilateral transtibial amputee.Study design: Single study with post experimental design.Methods and measures: Two different suspension systems such as supracondylar and cuff suspension for below knee prostheses were tested on 30 adults with unilateral transtibial amputees. All subjects walked with prosthesis. Data regarding gait parameters and Locomotor capabilities index were measured. Gait parameters such as velocity, cadence, step length, stride length were evaluated by CDG gait analyser and walking abilities of the subjects were evaluated by locomotor capabilities index (LCI).Result: The results revealed that the statistical difference between two suspension systems is significant (p<0.05). Study suggested that using supracondylar suspension velocity, cadence, stride length and step length increased compared to cuff suspension. But value of Locomotor capability index was more in cuff suspension compared to supracondylar suspension which indicates use of cuff suspension reduces fear of falling and patients feels more secure.Conclusion: The findings of the study thus support the hypothesis that there were significant difference with different suspension systems on gait parameters and locomotor capabilities index.

Evaluation of Functional Mobility Outcomes Following Electrical Stimulation in Children With Spastic Cerebral Palsy

This study investigated the clinical feasibility of electrical stimulation in enhancing ankle dorsiflexion of the tibialis anterior muscle to improve mobility in children with spastic cerebral palsy. The intervention group received electrical stimulation therapy for 30 minutes and physiotherapy for another 30 minutes for 5 days a week, up to 12 weeks. Gait parameters, Gross Motor Function Measure, Physiological Cost Index, surface electromyogram, and electroencephalogram (EEG) data were recorded pre- and posttreatment. Data were compared with the control group, which received only conventional physiotherapy for 60 minutes. There was an increase in walking speed (17.67%) and Gross Motor Function Measure scores (2.1%) while the Physiological Cost Index value was decreased (19.7%). The analysis of features extracted from the surface electromyogram showed an increase in muscle strength and that of EEG showed increased motor activities. Hence, electrical stimulation combined with conventional physiotherapy improve gait, muscle strength, and motor activities in children with spastic cerebral palsy.