Use Of Heavy Liquids Research Articles

Application of X-ray computed tomography scanning in describing partition curves of dense medium cyclones

The partition curve is an important tool to evaluate the separation performance of mineral separators like dense medium cyclones (DMCs). This curve is constructed by float-and-sink (FaS) analysis which involves the use of heavy liquids and suspensions. This traditional technique is hazardous to the environment, laborious, and time-consuming. Here, a new technique using X-ray computed tomography (XCT) scanning was successfully developed and applied for describing the partition curve of a DMC at an Australia-based lead–zinc mineral processing plant. The DMC feed, concentrate and reject streams were sampled and sieved into several size classes. The chemical assays and averaged densities according to each class were analysed by X-ray fluorescence spectrometry and gas pycnometry, respectively. The partition behaviour was investigated by XCT analysis. A model was proposed to determine the mass yield value – an important parameter to define partition curves – by mass balance and reconciliation, which is generally unknown during the sampling of continuous separation processes. From the reconstructed XCT images, we obtained detailed information on individual particles such as volume, surface area, mass, and density. Cumulative mass distribution curves and partition curves of the DMC for different size classes were then constructed and agreed with the FaS analysis. Using the XCT technology can help overcome the issues of the traditional FaS analysis. Moreover, this technology would allow for evaluating DMC separation efficiency with continuous, online, and real-time monitoring and control.

X-Ray computed tomography for 3D analysis of gangue mineral rejection by gravity preconcentration of sulfidic gold ores

ABSTRACTSpecific gravity washability curves used in the coal industry to define the theoretical gravity separation efficiency can be used in the same way for evaluation of preconcentration operations in the metal mining industry. These theoretical metal recovery/gangue rejection curves, which establish the maximum in gravity separation efficiency, can be determined from three-demensional (3D) image analysis by high resolution X-ray microtomography (HRXMT) rather than by sink-float analysis using heavy liquid fractionation. In this way, the tedious, time-consuming, and toxic use of heavy liquids for laboratory sink-float analysis is avoided. In addition to the theoretical gravity separation efficiency curves by HRXMT, further 3D particle information on mineral composition and texture is obtained, including grain size distribution. Experimental HRXMT results for two sulfidic gold ores are presented and compared to the results from dense media cyclone experiments in order to evaluate the efficiency of gangue mineral rejection.

How to Prevent Retinal Shift after Rhegmatogenous Retinal Detachment Repair: A Prospective, Randomized Study

To evaluate the effect of intraoperative use of heavy liquid on retinal shift after retinal detachment repair. Prospective, randomized study. Patients who underwent pars plana vitrectomy for macula-off rhegmatogenous retinal detachment were included in the current study. Patients were randomized into 2 groups: group A included patients in whom heavy liquid was used during the procedure and group B included patients in whom no heavy liquid was used. Group A and B patients were reviewed after 3 weeks and after 6 weeks, respectively, and fundus autofluorescence (FAF) images were obtained to visualize the retinal rotation. Postoperative macular shift, visualized with FAF. A total of 50 eyes from 49 patients were included. Overall, retinal shift was observed in 17 patients (34%). Patients in whom heavy liquid was used during the procedure showed significantly less macular shift after surgery (P= 0.049). There was a strong association between retinal shift and postoperative symptoms of metamorphopsia. Ten of 17 patients with retinal shift reported distorted vision (P < 0.001). The use of intraoperative heavy liquid seems to be associated with lower occurrence of retinal shift after retinal detachment repair.

Air tamponade and without heavy liquid usage in pars plana vitrectomy for rhegmatogenous retinal detachment repair.

To report the results of rhegmatogenous retinal detachment (RRD) repair after pars plana vitrectomy (PPV) without operative use of heavy liquid, and utilizing air tamponade in selected cases. RRD patients without severity of proliferative vitreoretinopathy C2 or more underwent PPV without operative use of heavy liquid, and utilizing air tamponade were consecutively enrolled. Alternative postoperative facedown position or lateral position was required for 3-5d. Totally 36 eyes of 36 patients (24 males, 66.7%) aged 53.8±10.9y underwent this modified surgery. The mean number of retinal break was 2.1±1.3. Most of the eyes (29, 80.6%) had retinal detachment involving more than one quadrant. Twenty-two (61.1%) eyes with cataract had combined phacoemulsification and intraocular lens implantation. The mean follow up time was 4.6±1.8mo. Two eyes with retinal redetachment underwent a second retinal repair surgery with silicone oil tamponade, yielding the primary reattachment rate to 94.4% (34/36). Six (16.7%) eyes had intraocular pressure higher than 25 mm Hg. The visual acuity (logMAR) improved from 0.98±0.74 preoperatively to 0.52±0.31 postoperatively (P<0.001). The success rate of this modified retinal repair surgery is comparable with traditional surgery. This technique can be considered for certain retinal detachment patients, since its apparent advantages included lower surgical complications, reduced surgery expenditure, shorter time for postoperative facedown position, and avoiding silicone oil removal surgery.

This issue of ACTA

The cover illustration shows a prolene thread inserted into Schlemm′s canal as reported by Grieshaber et al. in this issue of Acta. Klemp et al. in Copenhagen describe exudative retinal detachment, cataract formation and melanocytic tumours as the characteristic ocular findings in uveal melanocytic proliferation. Campos et al. in Portugal consider the role of the choroid in diabetic macular oedema and how OCT studies of the choroid advance this field of research. Jørstad et al. in Oslo found positive results with aflibercept in AMD eyes which were resistant to ranibizumab and bevacizumab injections. Many eyes required more than bimonthly aflibercept injections. Vujosevic et al. in Italy emphasize inflammatory biomarkers in diabetic macular oedema such as hyperreflective retinal spots, subfoveal neuroretinal detachment and increased foveal autofluorescence. These biomarkers improved with dexamethasone treatment. Subhi and Lykke Sørensen in Denmark correlated systemic leucocyte activity with onset and size of neovascular lesions in AMD. They suggest that inflammation plays a role in the pathophysiology. Sauer et al. in Germany used fluorescence lifetime imaging to map pigment distribution and evaluate its role in macular hole formation. Hamoudi et al. in Denmark found no difference in corneal endothelial density between combined and separated phacoemulsification and vitrectomy for epiretinal membrane. Makdoumi et al. in Sweden and the USA used blue light and riboflavin to kill resistant staphylococci and suggest this approach may work in corneal infections. Margulis et al. in the Netherlands, Spain and Denmark examined use of nonsteroidal anti-inflammatory eye drops. These were used with cataract surgery and for allergic conjunctivitis. Pärssinen and Kauppinen in Finland found astigmatism to increase with myopia. Corneal astigmatism predominates. Grieshaber et al. in South Africa and Switzerland recommend the Stegmann Schlemm′s canal expander to lower intraocular pressure in patients with moderate to advanced open angle glaucoma. Quérat and Chen in Sweden recommend ICARE® self-tonometry. Day-to-day variations are seen in most patients. Mrowicka et al. in Poland propose that insufficient antioxidant capacity may play a role in age related macular degeneration. This hypothesis is based on study of enzymes and genes related to antioxidant activity. Pilat et al. in UK used hand-held OCT to image anterior segment dysgenesis in children. The following articles are published electronically only and are accessible on www.actaophtalmologica.com, where you can also access the printed articles. Nitta et al. in Japan report an increase in retinal oximetry readings in retinal venules following glaucoma surgery and lowering of intraocular pressure. Tanito et al. in Japan recommend microhook trabeculotomy in glaucoma patients. It lowers IOP and reduces need for glaucoma medications. Mansouri and Shaarawy in the USA and Switzerland fond similar outcomes with scanning laser trabeculoplasty and selective laser trabeculoplasty. Lanza et al. in Italy used light backscattering with in vivo corneal confocal microscopy to evaluate changes in corneal layers in patients with Sjögren syndrome and dry eyes. Shimada et al. in Japan found reduced anterior chamber bacterial contamination with either 0.025% povidone-iodine or 0.0025% polyvinyl alcohol iodine irrigation of ocular surface. Peiretti et al. in Italy, the Netherlands, Saudi Arabia and the USA examined retinal folds following retinal detachment repair. This was not influenced by use of heavy liquids in surgery or postoperative positioning. Chan et al. in Hong Kong, Singapore and UK seek ways to measure and control emulsification of intraocular silicone oil. Kang et al. in Korea measured greater choroidal thickness in eyes with vitreoretinal traction. This was reversed following epiretinal membrane surgery and release of the traction. Jonas et al. in India and Germany found myopic retinopathy to be rare in rural India. It was associated with open angle glaucoma. Carreño et al. in Spain, USA and UK measured several inflammatory cytokines in tear fluid in uveitis patients. Bray et al. in UK suggest that portable electronic vision enhancement systems are cost-effective to improve near vision. However, it may not provide cost-effective improvement in quality of life. Babeau et al. in France comment on an article on using adaptive optics for screening chloroquine retinopathy. Parrovano et al. in Italy used OCT angiography to monitor reduction in neovascular lesions. Van Asten et al. in the Netherlands found positive outcomes with aflibercept in AMD patients unresponsive to bevacizumab. Lytvynchuk in Ukraine surgically removed a retinal branch artery embolus. Dimopoulos et al. in Germany used autologous thrombocyte serum for macular hole surgery. Grewal et al. in USA used intraoperative OCT to guide placement of Argus II retinal prosthesis. Huynh et al. in the USA found no benefit from dilated fundus examination in patients with spontaneous subconjunctival haemorrhage. Qu-Knafo et al. in France suggest that eyes with DME and serous retinal detachment may show greater improvement with ranibizumab than eyes without serous detachment. I hope you are enjoying a pleasant summer and Acta fits into your summer reading schedule.

Water based fractionation of particles

A feed of particles covering a wide range of particle sizes and densities was placed into a novel separator, referred to as the Reflux Classifier, and fractionated at a series of fluidization velocities. Double fractionation was then achieved when each product was sieved into narrow size fractions. For the coal particles used in this study, the ash % was determined for each of the samples. The ash % correlated strongly with particle density, and hence was a useful proxy for the particle density. A new Fractionation Algorithm was developed, which provided a method for estimating the feed size and density distribution from the Double Fractionation data. The cumulative yield % versus the cumulative ash % curves for each size fraction, and for the overall feed were then determined. The findings from the study were validated against accurate results obtained using the sink-float method. Excellent agreement with the curves obtained using the sink-float method was obtained. The sink-float method requires the use of heavy liquids; these are invariably toxic and expensive, hence a viable alternative is needed. The water based fractionation method, in conjunction with the Fractionation Algorithm, may prove to be a suitable substitute for the sink-float method. Precise details of the method and algorithm are therefore provided in order to permit the adoption of this new approach by other laboratories.

Simultaneous Extraction of Phytoliths, Pollen and Spores from Sediments

Archaeological sediments often offer opportunities to examine local palaeoenvironmental conditions from analysis of included microfossils. On-site conditions commonly vary, and thus so do the preservation conditions for microfossils. Consequently, a range of palynological preparation techniques are commonly used. While different types of microfossils provide valuable palaeoenvironmental information, the use of separate extraction methods for different microfossil types may be both time- and resource-consuming, especially where the recovery predicability is low. This paper examines the possibility of combining preparation techniques for three commonly encountered microfossils—pollen, spores and phytoliths—by comparing pollen extractions using heavy liquid extraction and standard pollen recovery procedures. Although the use of heavy liquids for pollen and spore preparations has been well-documented, for several reasons it has not been a favoured technique for pollen extraction. The research reported here shows that for most of the sediments tested, heavy liquid extraction procedures produced comparable results to those arising from standard pollen extraction techniques. For oxidized sediments, especially, more reliable results are likely to be obtained from heavy liquid extraction procedures than from those employing acetolysis. Overall, heavy liquid procedures allow complementary suites of data to be investigated with the least cost and effort, thus enabling palynologists and phytolithologists to adopt more effective research practices for environmental reconstruction.

Removal of lens fragments from the vitreous cavity.

Between March 1993 and September 1994 we treated 25 cases of lenses in the vitreous cavity. Nineteen of the 25 were the result of dislocation during phacoemulsification. During this time, we adopted a single surgical algorithm involving vitrectomy, heavy liquids and ultrasound fragmentation. The aims of this retrospective study were to test the validity of our surgical algorithm and to report on outcomes and complications. The indications for vitreous surgery were raised intraocular pressure, uveitis and poor vision. Vitreous surgery was carried out at a mean of 29 days following phacoemulsification. Six patients required heavy liquids and 5 needed ultrasound fragmentation. Vitreous surgery undertaken less than 17 days after phacoemulsification had an increased likelihood of requiring heavy liquids and/or fragmentation (p < 0.02). The greatest threat to a favourable visual outcome was retinal detachment, which was significantly associated with fragmentation and use of heavy liquids (p < 0.02). The presence of an intraocular lens (IOL) reduced the surgical options for removal of the lens fragments, and IOL should not be inserted where lens matter dislocates. The study suggests that we should avoid fragmentation and, provided the intraocular pressure and uveitis can be controlled, that vitreous surgery should be deferred for 2-3 weeks following phacoemulsification.

Mathematical modelling of retinal tear formation: implications for the use of heavy liquids.

When force is applied to detached retina it elevates, stretches, and becomes irreversibly deformed. Finally it tears, and the timing and location of tear formation are determined by the distribution of stress within the retina. This stress distribution is dependent upon the retinal contour. We have tested this using retinas of freshly enucleated bovine eyes. A suture was attached to isolated retinal tissue using butylacrylate (Histoacryl) glue and traction was applied to this suture so stretching the retina. We present a mathematical model of the in vitro data obtained, with predictions for local retinal internal tensions. We show that these are altered by the addition of hydrostatic forces due to the presence of heavy liquids. These findings have implications for epiretinal membrane dissection during surgery and for the use of heavy liquids during membrane peeling.

Flow Chart for Mineral Separation From Granitic Rocks

The article provides a flow chart for the separation and purification of major, minor, and accessory minerals from granitic rocks. With careful use of heavy liquids, and a Franz Isodynamic Magnetic Separator, it is possible to obtain mineral concentrates with a purity of 95 percent or better.

Atmospherically transported volcanic glass in deep-sea sediments: development of a separation and counting technique

A new method to separate fine, disseminated volcanic glass from deep-sea sediments and to measure its accumulation rate is described. Separation is by use of heavy liquids with an efficiency that ranges from 45 to 85% with increasing particle size. The size distribution of the bulk sediments and weights of selected volcanic glass size ranges are measured using a Coulter Counter and Cahn Electrobalance. A scanning electron microscope and a high-power transmitted light microscope have been used to estimate the volcanic glass load of the 11- to 1-μm size range. The reproducibility of results from split samples is between 0·10 and 6·5%. The precision is generally higher for those samples containing larger amounts of the fine volcanic glass (36-11 μm). A 6-cm 3 wet sediment volume, with 2-cm vertical extent, representing from 2000 to 6000 years of depositional time, is an ideal sample size for this separation and counting system.

Density and Refractive Index Studies of Dental Hard Tissues

A rapid, quantitative method for the separation of the enamel, dentin, and cementum of a single tooth to obtain samples of known purity will permit the following investigations: 1) Normal values and ranges of variation in the composition of enamel and dentin. 2) Changes in composition associated with caries (5), pyorrhea or disturbances in nutrition, metabolism or endocrine balance. 3) Proportion of enamel to dentin in normal, hyperand hypoplastic teeth and changes due to attrition, erosion or caries. Methods for obtaining pure dentin or enamel by heating or grinding are unsatisfactory because of the time required and the incomplete recovery. The method described by Brekhus and Armstrong (3), based on the use of heavy liquids with density intermediate between dentin and enamel, offers a distinct improvement over previous methods, but leaves a few things to be desired. For instance, it would be advantageou§ to have (a) a more rapid method, (b) a check on the purity of the enamel and dentin fractions, and (c) an avoidance of filtration. According to the literature, a centrifugal separation method would seem to be desirable, especially when working with fine powders. Bernal and Crowfoot (2) found centrifugation to give a more accurate

Specific gravities of minerals: an index of some recent determinations

As a first-aid in the identification of non-metallic minerals I have for many years made use of specific gravity, which is a character that can be easily and rapidly determined hy the use of heavy liquids. A small, clean fragment of the mineral to be tested is dropped into one or other of a series of tubes containing methylene iodide with various small known Crystals as indicators. Adding benzene from a dropping-bottle, the density of the liquid is quickly brought to that of the mineral. This preliminary determination of the specific gravity gives a useful clue as to the nature of the mineral—what it may or may not be ; and the same fragment can then be used for confirmatory optical and micro-chemical tests.