Refractoriness of Certain Gold OrestoCyanidation: Probable Causes and Possible Solutions

Cyanidation has established itself as the main process for extracting gold from ores in this century. However, many ores exhibit refractoriness to the conventional cyanida-tion process. The main cause of the refractoriness is generally the presence of carbon, tellurium, and sulfides, particularly those of antimony, arsenic, and iron. The problem is usually solved by either modifying the cyanidation conditions or providing an oxidation pretreatmerrt

This paper presents results from studies that help in understanding the causes of refractoriness of various gold ores. This is followed by a discussion of many processes that have been developed to solve the problem such as intensive cyanidation, pressure cyanidation, carbon-in-leach cyanidation. and prctreatment processes such as roasting, chemical oxidation, autoclave oxidation, and bacterial oxidation.     

AN INTEGRATED PROCESS FOR THE RECOVERY OF TUNGSTEN AND TIN FROM A COMBINED WOLFRAMITE–SCHEELITE–CASSITERITE CONCENTRATE

This article presents results of the studies on development of viable process route for quantitative recovery of tungsten and tin values occurring together in the form of a multimineral concentrate of wolframite, scheelite, and cassiterite. The investigations were carried out using a tin–tungsten multimineral ore from Kyrgyzstan (Central Asia). Tungsten minerals in this ore occur both as distinct liberated mineral phases and as composites, viz. ultrafine dissemination of wolframite in scheelite and vice versa. Cassiterite also has similar characteristics, albeit to a lesser extent, with few grains containing ex-solution intergrowth of columbite/tantalite and very fine dissemination of tungsten minerals in its lattice. The complex nature of occurrence of both tungsten and tin minerals necessitated an integrated process comprising physical beneficiation and chemical extraction. The process route that was developed gave a tungsten and tin recovery of about 80 and 90%, respectively, on treating a primary gravity preconcentrate analyzing 16.5% WO₃ and 25.7% Sn.     

SWELLING STRESS AND HYDROSTATIC COMPRESSIBILITY OF GROUND CORN AND ITS CONSTITUENTS

Swelling stresses and hydrostatic compressibilities of ground whole corn, endosperm and germ were determined by using the theory of swelling stresses in gels. The ground corn and its constituents were considered as gels. The magnitude of swelling stresses in the ground corn materials was in order of several thousand pounds per square inch at low equilibrium moisture contents, when subjected to increased vapor pressure. The hydrostatic compressibility for ground whole corn, endosperm and germ increased with an increase of moisture content.     

Network Competition and Industry Structure

The prevailing trend in the US telecommunications industry istoward industry convergence and market competition. This paperexamines possible scenarios for developments in the telecommunicationsmarket as a result of further industry convergence and changesin the political and regulatory environments toward competition.It studies the cost structures of the industry under a hierarchicallayered network architecture framework and addresses some potentialeconomic problems. Vertical and horizontal integration may bea natural outgrowth of competition in the converging industries.The paper concludes with a call for clearer economic analysisof future market structure on behalf of public policy makers,particularly with regard to quantification of underlying changesin consumers‘ purchasing behavior and providers’cost structure.     

Modeling Flow in Cylindrical Extruder Dies

Volumetric flowrate was studied in the die of a single screw extruder. Variables included the ratio of die length to die diameter, barrel to die diameter, barrel and die temperature, screw speed and product moisture. Die conductance was determined graphically and analytically. Results indicated that for a constant pressure drop across the die, increasing temperature, die diameter or moisture increased flowrate. Dimensional analysis was used to study the effect of each parameter on the flow through the extruder die. An expression for temperature rise due to viscous dissipation for isothermal flow in the die was developed and nomographs are presented.     

Mechanical behavior of organo-modified Indian bentonite nanoclay fiber-reinforced plastic nanocomposites

The aim of the research was to examine the influence of organo-modified Indian bentonite （IB） nanoclay dispersed in vinyisster on the mechanical properties of nanoclaylvinylesterlglass nanocomposRes. Nanoclay was organically modified using cationic surfactant hexadecyltrimethylammonium bromide （HDTMA-Br） by cation exchange method and dispersed in vinylester using ultrasonication and twin screw extrusion. XRD of nanoclaylvinylester revealed exfoliaUon at 4 wt.% nanoclay indicating uniform dispersion in the polymer. DSC results showed improvement in glass transition temperature by 22.3% in 4 wt.% nanoclaylvinylester/glass when compared with that of vinylester/glass. Nanoclay/vinylester/glass with 4 wt,% nanoclay showed 29.23%, 23.84% and 60.87% improvement in ultimate tensile strength （UTS）, fiexural strength （FS） and interlaminar shear strength （ILSS） respectively when compared with those of vinylester! glass. The mode of tensile failure examined by SEM showed no agglomeration of nanoclay in 4 wt.% nanoclayNinylester/glass specimens.     

Effect of laminate thickness on moisture diffusion of polymer matrix composites in artificial seawater ageing

The influence of laminate thickness of polymer matrix composites on moisture diffusion in seawater immersion, as well as the resulting mechanical property degradation for composites of glass/isopolyester (G/IPE), carbon/isopolyester (C/IPE), glass/vinylester (G/VE) and carbon/vinylester (C/VE), was investigated in this paper. Laminates 3 and 10 mm in thickness, fabricated using the wet hand lay-up technique, were characterized for moisture absorption in artificial seawater medium, and their flexural strength and interlaminar shear strength (ILSS) degradations were studied. Moisture diffusion was observed to be anamolous to the Fick’s law for both 3 and 10 mm thick samples in the later stage of diffusion. Moisture permeability of 10 mm thick samples was two to three order greater than that of 3 mm thick ones, while the time to moisture saturation remained unchanged. With the increase of laminate thickness, moisture saturation increased by 1.4% for C/VE and 7% for G/IPE. The residual flexural strength and ILSS were greater in case of 10 mm thick specimens after 200 days of exposure. SEM examination of the fractured specimens showed greater levels of fibre/matrix debonding in 10 mm thick specimens.     

Mechanical,thermal and fire retardation behaviours of nanoclay/vinylester nanocomposites

The dispersion of montmorillonite (MMT) in vinylester for preparing nanoclay/vinylester gel coat was reported. Two sets of MMT/vinylester specimens, namely Type 1 and Type 2, were prepared for comparative studies. Type 1 specimens were prepared using ultrasonication only, and Type 2 specimens were prepared using both ultrasonication and twin-screw extrusion. According to XRD and TEM results, Type 2 specimens showed lower levels of nanoclay agglomeration and higher levels of exfoliation. DSC results showed that the glass transition temperatures of Type 2 specimens are higher than those of Type 1 specimens. TGA results showed that the residual weight of 4 wt.% MMT/vinylester of Type 1 was 7.38%, while the corresponding value of Type 2 was 13.5%, indicating lower thermal degradation in the latter. MMT/vinylester/glass and MMT/vinylester/carbon specimens were fabricated and tested for mechanical and fire retardation behaviours. Type 2 based nanocomposite laminates showed greater values of ultimate tensile strength, flexural strength, interlaminar shear strength, impact strength, horizontal burning rate, and vertical burning rate than Type 1 based laminates. SEM images of tensile fractured surfaces revealed that Type 2 based laminates have no or less agglomeration of nanoclay than Type 1 based laminates.     

On the simulation of continuous non-linear filters A comparative study of second- and third-order approximations

Among several second-order approximations to the filter of a non-linear system, it is found that the extended Kalman filter is generally the most versatile. The second-order likelihood filter, also known ns the Detchmendy—Sridhar filter is inferior to the ahove and at the same time involves more computation. In the special ease when analytical expressions For the gaussian expectation integrals of the non-linearities can be found, the extended Kalman filter can be further improved by using stochastic linear approximations as suggested by Sunahara. The third-order likelihood filter derived in this paper is more accurate than the above, but calls for considerable storage space and computing time.