Precipitation of ions

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Oxidation is a process in which one or more electrons are transferred from the chemical being oxidized to the chemical initiating the transfer. The main purpose of treating wastes by oxidation is detoxification. Oxidation can also aid in the precipitation of ions in cases of oxidized ions that have a solubility lower than that of the original ions. 

As mentioned in Chapter 10 on water softening, as long as the concentrations of CaCOs and Mg(OH)2 exceed their solubilities, the solids may continue to precipitate. This condition can cause scale to form, a solid that deposits due to precipitation of ions in solution. To prevent scale formation, the water must be stabilized. A water is said to be stable when it neither dissolves nor deposits precipitates. If the pH is high, stabilization may be accomplished using one of several acids or using CO2, a process called recarbomtion. If the pH is low, stabilization may be accomplished using lime or some other bases. 

Specific Binding and Surface Precipitation of Ions and Ligands... 

Table 3.1. Precipitation of ions as hydrous oxides at various pH values...

NOTE Precipitation of ions listed without an x is usually not pH-dependent. 

Fractional Precipitation of Ions as a Function of the Solution s pH Value... 

Fig 1. Extraction and precipitation of ions in a setting glass-ionomer cement. 

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