Cementation precipitation processes

The first equation is an example of hydrolysis and is commonly referred to as chemical precipitation. The separation is effective because of the differences in solubiUty products of the copper(II) and iron(III) hydroxides. The second equation is known as reductive precipitation and is an example of an electrochemical reaction. The use of more electropositive metals to effect reductive precipitation is known as cementation. Precipitation is used to separate impurities from a metal in solution such as iron from copper (eq. 1), or it can be used to remove the primary metal, copper, from solution (eq. 2). Precipitation is commonly practiced for the separation of small quantities of metals from large volumes of water, such as from industrial waste processes. 

Hydraulic cements. These cements are formed from two constituents one of which is water. Setting comprises a hydration and precipitation process. Into this category fall Portland cement and plaster of Paris. 

The precipitation process for gold from cyanide solution by zinc is chemically a simple metathesis, or cementation reaction ... 

The recovery or removal of metals from solutions derived from the leaching of minerals is an important step in any hydrometallurgical process. Precipitation by reduction to the metallic state in electrochemical cells will be discussed in Section 63.3.5 this section will cover the use of chemical reagents to control the precipitation process. Therefore, although the production of metallic powders by the reduction of metal ions with hydrogen or less-noble metals (cementation) is electrochemical in nature, it will be discussed under this heading. 

The fact that the hydrogen ion is an important chemical species in these reactions is indicative of the major role that carbonic acid plays in influencing the pH and buffer capacity of natural waters. Furthermore, the activity of the carbonate anion in part determines the degree of saturation of natural waters with respect to carbonate minerals. Determination of the activity or concentration of CO32- is not an easy task nevertheless, it is necessary to the interpretation of a myriad of processes, including carbonate mineral and cement precipitation-dissolution and recrystallization reactions. 

The formation of beachrock will be examined as an example of carbonate cement formation, because it has been extensively investigated and because it represents a chance to study carbonate cement emplacement under conditions where the rate of cement precipitation is relatively rapid and the associated solutions can be analyzed directly. It also differs from the cementation process in our model in that carbon dioxide can be degassed to the atmosphere, resulting in major changes in the saturation state of the cementing solution. 

Sedimentary rock—Rock formed by deposition, compaction, and cementation of weathered rock or organic material, or by chemical precipitation. Salt and gypsum form from evaporation and precipitation processes. 

Cementation the process of precipitation of a binding material around grains or minerals in rocks. 

The concentrations of Fe, Mn, and Mg in calcite cements are often used to interpret their depositional environment. These interpretations use distribution coefficients to estimate the composition of the solution based on an analysis of the calcite cement. Laboratory determinations of these distribution coefficients are typically carried out in batch reactors. Creating a model of the precipitation process in these experiments is helpful for understanding the uncertainties associated with the measurements. If the calcite is precipitated in a batch reactor, Eq. (8.40)... 

Cement hydration Reaction of the anhydrous cement phases with water to form cement hydrates. The reaction is a dissolution-precipitation process involving both the participation and the mediation of an aqueous phase. 

The development of electrostatic precipitators soon led to new applications, including the separation of metal oxide fumes. This was followed by various metal manufacturing processes such as the lead blast furnace, ore roaster, and reverberatory furnace. Electrostatic gas cleaning was soon applied also in cement kilns and in several exotic applications, such as recovering valuable metals from exhaust gases. 

Zement-kalk, m. hydraulic lime, -kalkmdrtel, m. lime-and-oement mortar, -kalkstein, m. hydraulic limestone, -kohle, /. cementation carbon, -kufe, -kiipe, /. cement (or concrete) vat. -kupfer, m. cement copper, -mastiz, m. mastic cement, -metoll, n. metal precipitated by the cementation process. -miUk, /. thin cetnent mortar. 

Waste Treatment. Figure 2 outlines the current waste recovery and treatment processes, and proposed changes. Acid waste streams are sent through nitric acid and secondary plutonium recovery processes before being neutralized with potassium hydroxide and filtered. This stream and basic and laundry waste streams are sent to waste treatment. During waste treatment, the actinides in the aqueous waste are removed by three stages of hydroxide-iron carrier-flocculant precipitation. The filtrate solution is then evaporated to a solid with a spray dryer and the solids are cemented and sent to retrievable storage. 

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