Thermodynamic Interpretation on the Rheology of Aqueous Bentonite Suspensions

Since their exceptional rheological behavior, bentonite suspensions are widely used in engineering, industrial, agricultural, and drilling applications. So, the aim of the present study is to investigate the rheological properties of three types aqueous suspensions prepared with calcium bentonite (CaB), sodium bentonite (NaB) obtained from that by Na2CO3 activation, and NaB with the excess soda. The CaB taken from Giresun/Turkey region contains calcium smectite (CaxS) as clay mineral and opal CT (SiO2.nH2O) as impurity which is paracrystalline silica. Soda content by the activation and bentonite content in the suspension were changed in the interval of 2.5-15.0% and 5-20% by mass, respectively. CaxS completely converted to sodium smectite (Na2xS) by the activation with the soda content of 2.5% and then Na2xS+Na2CO3 mixtures formed. Rheological properties of these aqueous suspensions were measured using a Fann Viscometer. These properties reached their maxima by the most thixotropic Na2xS suspensions and greatly increased with the increasing of smectite content. Rheological plots drawn of the shear rate vs. shear stress in the interval of 170-1020 s-1 showed that the suspensions flow as a Bingham Plastic. Change in rheological properties depending on the smectite type and content as well as excess soda content was explained thermodynamically based on the chemical potential gradient between interlayer and dispenser waters.

Ring removal in rotary kilns used by the pulp and paper industry

Ring formation occurs in the rotary kilns used by the pulp and paper industry to regenerate the lime needed to produce white liquor. The main rings are: burning zone rings, mid-kiln rings, dust rings and/or mud balls, and mud rings. While the exact mechanisms of ring formation are not completely understood, frequent changes in the production rate and the mud solids, high soda content in the mud, and high levels of dust are believed to play a major role in ring formation. The presence of rings can restrict the movement of material through the kiln. If undetected, this can result in overheating of the refractory lining. In the worst case, the presence of rings can lead to unscheduled downtime to clean out the ring and replace damaged refractory bricks. Depending on the severity, the cost of repairs and lost production can be in excess of US$3 million for a single event. Even if the root cause of ring formation is known, from a practical standpoint, it can be difficult to eliminate rings. In mills where ring formation is a recurring problem, mechanical ring removal systems should be considered. This paper describes the use of ring removal systems as a cost effective way to mitigate the problems associated with ring formation.

Soda and Aluminum Recovery from Spent Etching Baths by Aqueous Precipitation

The aluminum anodising industry is an important industrial sector that produces great amounts of polluted effluents, which after treatment generate sludge. This fact brings environmental and economical concerns to the companies. Best way to deal with the problem, according to the “prevention strategy” set by the European Directive on Integrated Pollution Prevention and Control, is to implement preventive techniques and technologies to optimise the use of resources and minimise losses, and in turn waste. Among the operations of an anodising line, the etching/satinising stage is responsible for the production of a huge quantity of wastewater neutralisation sludge and for the wrong use of caustic soda. “Caustic etch recovery” technology is claimed to drastically reduce the generation of neutralisation sludge and the purchasing of fresh caustic soda by regenerating the exhausted etching/satinising solution, through an aqueous precipitation reaction. This paper presents the capability of the technology to effectively regenerate the exhausted caustic solution, and investigated the parameters with major effect on the process yield, in order to optimise it. It was demonstrated that the technology effectively recovers the solution, increases its soda content and diminishes the dissolved aluminum content by precipitation. Moreover the conditions that optimise the process are simple and inexpensive. After treatment the solution present the properties to be recycled in the etching/satinising operation.

Experimental Research on Strengthen Mechanism of NaOH on Light Wall Materials Prepared from Crushed Brick Powder

Crushed brick light weight wall material, which was made of crushed brick as a main raw material and P•S cement as a cementious material. Crushed foam glass and some admixtures were added, is prepared under the ordinary temperature and pressure condition. The main research in this paper is if NaOH has good alkaline excitation on crushed brick light weight wall material through experimental research and mechanism analysis. Studies have shown that: (1) The main chemical composition of crushed brick powder are SiO2 and Al2O3, crushed brick powder have a certain activity.(2) NaOH releases the activity of the internal soluble SiO2 and Al2O3.(3) In this experiment system, when the caustic soda content is about 3%, there has been an obvious peak of compressive strength.

Geochemistry and Radioactivity of Mineralized Pegmatite from Abu Rusheid Area, South Eastern Desert, Egypt

The mineralized pegmatite of Abu-Rusheid area, S. Eastern Desert, has quartz core and feldspars and mica margins. This pegamtite was analyzed by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to determine the content of the major and trace elements including the rare earth elements (REE). The mineralized pegmatite vein trends NNW-SSE with dip of about 10- 30° due WSW. It is emplaced parallel to foliation and banding of the cataclastic country rocks. The studied pegmatite is classified as rare metals-enriched and shows a zonal distribution from the barren core to the mineralized wall-zone in the metals; Nb, Ta, Zr, Hf, Th, U, Y and Ga. The main carriers of the trace metals are zircon, rutile, columbitetantalite, samarskite and other REE and Th-U minerals. Cassiterite, chlorite, deep violet fluorite, calcite, goethite, hematite, pyrite, magnetite, zinnwaldite, and phlogobite, are the main accessory minerals. The studied pegmatite is highly differentiated, NYF-type and characterized by high FeO/MgO ratio with high concentration of Nb, Y, Zr, Th, U, REE (except Eu), and Ga. It is derived from Fenriched proterozoic crustal source depleted in Cs, B and P. The rock is peraluminous and highly fractionated and had been affected by hydrothermal alteration. The pegmatite displays clear M-type tetrad effect of the REE. The calculated tetrad effect in the pegmatite of Abu-Rusheid demonstrates clear tendency towards the ratios of the common isovalents such as Zr/Hf, Nb/Ta and Y/Ho. However, the tetrad effect seems not to be mutual with the content of Na2O and Rb/Sr. The absence of coherence between tetrad effect and soda content may indicate insignificant role of the Na-metasomatism in developing the tetrad effect. The pegmatite has a prominent negative Eu anomaly and excessively low K/Rb ratio. The radioactivity of the studied pegmatite is related to a) uranium mineral (autunite), b) thorium minerals (thorite, thorianite and uranothorite) and c)