Hydration leaching

With the change in surface area and porosity, acid activation invariably affects acidity of the catalysts. Acidity as measured by STPD of ammonia is given in fig.2. Initially, an increase in the total acidity is observed with the increase in activation time however there is not much change observed after 2h activation. It is well known that the hydrated leached... 

This report describes the degradation of concrete stmctures, that is, mainly stmctures over thousand years and about ten thousand years old with a history longer than that of Portland cement, due to soft water. In the underwater environment of radioactive waste repositories especially, as shown in Fig. 1, cement hydrates leach into the groundwater. An overview of the methods to predict degradation and methods to suppress degradation, with the focus on the phenomenon of degradation of cementitious material, is described here. 

It is known from the past that hydrates leach from concrete. Taylor [21] has proposed various measures against leaching by using Pozzolanic materials, alumina cement, dense concrete, carbonated concrete, autoclave curing, and so on. Even ancient concrete used 5000 years ago in China [22] did not use steel the cement close to today s low-heat Portland cement had carbonated, and had helped to maintain the long-term soundness of the material. Based on such information, the leaching resistance of carbonated concrete and Pozzolan material was evaluated. The dissolution equilibrium relationships... 

A.lkaline Solutions. The most important example of alkaline leach is the digestion of hydrated alumina from bauxite by a sodium hydroxide solution at 160-170°C, ie, the Bayer process (see Aluminumand aluminum alloys). 

The foHowing factors are important in dump leaching (/) the role of bacteria (2) the appHcation of acid to prevent or delay precipitation of hydrated ferric sulfate (J) oxidation to remove excess iron from mine water in settling pools, as shown in equations 38 and 39 (4) optimization of dump configuration for good solution distribution and (5) avaHabHity of oxygen. 

Crisp Wilson (1974b, 1976) attributed the slowness of binding in the case of aluminium to several effects preferential leaching of calcium ions, lack of mobility of the hydrated or multinuclear aluminium species... 

Subsequently, the dried ore is reduced in an electric furnace to ferronickel. Drying of the ore ensures smooth operation in the reduction furnace. As another example, reference may be drawn to the processing of kaolinite, Al2(Si05)(0H)4, for the recovery of alumina. The mineral is leached with dilute sulfuric acid. In the hydrated form, the mineral is insoluble in dilute mineral acids, and on drying at 400 to 800 °C, kaolinite is converted to the amorphous form, metakaolin, A1203 2 Si02 ... 

Water is the most common solvent used to dissolve ionic compounds. Principally, the reasons for dissolution of ionic crystals in water are two. Not stated in any order of sequence of importance, the first one maybe mentioned as the weakening of the electrostatic forces of attraction in an ionic crystal known, and the effect may be alternatively be expressed as the consequence of the presence of highly polar water molecules. The high dielectric constant of water implies that the attractive forces between the cations and anions in an ionic salt come down by a factor of 80 when water happens to be the leaching medium. The second responsible factor is the tendency of the ionic crystals to hydrate. 

Alumet A process for extracting alumina and potassium sulfate from alunite ore (a basic hydrated potassium aluminum sulfate) involving reductive calcination and alkali leaching. Developed and piloted by the Alunite Metallurgical Company, UT, in the mid 1970s but not commercialized. See also Kalunite. 

In the extraction procedure for sediments an initial leach with 6M hydrochloric acid was used in order to remove the bulk of carbonate and hydrated oxide phases before extraction with sodium hydroxide solution. This procedure gave a recovery of ca. 70% of the total arsenic in the sediment as determined following total decomposition. 

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