1. e. While the breakdown of gelular resin beads because of dehydration surface cracking during saturated (26 percent) brine regeneration (osmotic shock) is generally not great, reducing the brine concentration to 10 to 12 percent can reduce osmotic shock breakdown and extend the life of cation exchange resin beads. Also, the dilution of brine provides greater volume of brine, which aids a uniform contact of brine solution with all the resin, particularly at the lower, more salt efficient regenerant levels.
2. False. It is true that at least 30 minutes of brine contact time with the resin is desirable. However, at flow rates much below 0.25 gpm/ft3, it can be more difficult to obtain good brine distribution throughout all of the resin bed, because the brine is a higher density than water and it may more readily take the course of least resistance and channel through the resin bed.
3. d. At 2 percent brine concentration, for example, the hardness exchange capacity would be approximately 90 percent of what it would be at 10 percent brine concentration. There are expected reductions in exchange capacity and regeneration efficiency, and expected higher hardness leakages with the use of very dilute brine below 10 percent NaCl concentration.
4. c. Part of the sacrifice in capacity is caused by the sea water's high hardness (5,500 milligrams per liter as CaCO3), which also reduces the regeneration efficiency and increases the hardness leakage in the service cycle.
6. a. Salt efficiency is obtained by dividing the grains of hardness exchange per pound of salt used. In 8 percent DVB cross-linked gel resin, about 21,000 grains of exchange capacity in a cubic foot of resin can be developed with 6 pounds of salt. Therefore, 21,000 divided by 6 = 3,500 grains of hardness exchange per pound of NaCl salt used.
9. True. Never add water to an acid. Always add the concentrated acid to water, with good mixing to prevent spattering and dangerous safety conditions. The heat generated even when acid is added to water can be considerable and high enough to cause deformation of thermoplastic pipes or parts. A good mnemonic is “do as you ‘oughta,’ add acid to ‘watah.’”
10. False. Nitric acid is seldom used as a regenerant in water treatment applications. Nitric acid (and other strong oxidizing agents) may cause explosive reactions when mixed with organic ion exchange resins.