Internal alkalinity generation

This chapter summarizes water chemistry changes and effects of acidification on biogeochemical processes. We focus on major ions and nutrients, discuss internal alkalinity generation and sediment ion-exchange processes, and present preliminary recovery models. Results for trace and minor metals and other chemical constituents are presented elsewhere (2-4). 

Several whole-lake ion budgets have shown that internal alkalinity generation (IAG) is important in regulating the alkalinity of groundwater recharge lakes and that sulfate retention processes are the dominant source of IAG (3-5)1 and synoptic studies (6-9) have shown that sulfate reduction occurs in sediments from a wide variety of softwater lakes. Baker et al. (10) showed that net sulfate retention in lakes can be modeled as a first-order process with respect to sulfate concentration and several "whole ecosystem" models of lake acidification recently have been modified to include in-lake processes (11). 

Treatment chemicals should preferably be fed to the FW tank to minimize sludge deposits in the coils. Hydroxide alkalinity in ppm (mg/1) CaC03 must be maintained at a sufficient concentration to keep silica soluble and avoid complex silicate deposits. These precautions are necessary because scale-control internal treatment chemicals usually are not employed to assist in the prevention of such deposits in coil-type steam generators. 

A prerequisite for all etch-stop techniques discussed so far is an electrical connection to an external power supply. However, if the potential required for passivation in alkaline solutions is below 1 V, it can be generated by an internal galvanic cell, for example by a gold-silicon element [As4, Xil]. An internal galvanic cell can also be realized by a p-n junction illuminated in the etchant, as discussed in the next section. Internal cells eliminate the need for external contacts and make this technique suitable for simple batch fabrication. 

Because sulfuric acid was used to acidify the treatment basin, the increase in SO4 2" was expected. However, only about 50% of the sulfate added as sulfuric acid remained in the water column of the treatment basin the remainder was lost to outseepage and in-lake processes. For example, had the added sulfate remained in the water column, [S042- ] at pH 4.7 would have been 257 xequiv/L (versus the measured [S042- ] = 147 ixequiv/ L). The loss of sulfate by reduction may contribute to the generation of alkalinity this possibility is discussed in the Internal Alkalinity section. Chloride showed no significant trend with decreasing pH. 

Aqueous Extract pH. The purpose of a deacidification treatment is to neutralize internally-generated carboxyl groups as well as acids from dyeing, finishing or exposure to the environment. Ideally an alkaline reserve should be deposited in the fibers to combat future acidity. Fabrics... 

In this section, details of an easily controllable, safe method for producing high-purity H2 gas are described. This method of generating H2 gas is particularly suitable for providing a clean source of H2 gas for use as an anodic fuel in fuel cells or as a fuel for internal combustion engines in transportation applications. This compact, portable H2 generator is based on a non-pressurized, aqueous solution of alkaline sodium borohydride (NaBH, tetrahydroborate). As found by Schlesinger et al.,1 when aqueous NaBH... 

The fundamental principle of SPE reactors is the coupling of the transport of electrical charges, i.e. an electrical current with a transport of ions (cations or anions), through a SPE membrane due to an externally applied (e.g. electrolysis) or internally generated (e.g. fuel cells) electrical potential gradient. For example, in a chlorine/alkaline SPE reactor (Fig. 13.3), the anode and cathode were separated by a cation-SPE membrane (e.g. Nafion 117) forming two compartments, containing the anolyte (e.g. 25 wt% NaCl solution) and the catholyte (e.g. dilute sodium hydroxide), respectively. 

---