filtration) increased the removals of hardness and activity to 87 an 96%, respectively, when 50 mg of excess lime and soda ash per lit were added.

8-1.7 Repeated-precipitation Process

Many conventional water-treatment plants with separate mixin coagulating, and settling basins can be modified readily to utilize th repeated-precipitation process proposed by McCauley and Eliassen. Suggested flow diagrams for the repeated-precipitation process (eithe the straight-line flow method or the upflow reaction or contact basins are reproduced in Figs. 8.6 and 8.7.

Modifications required for the successful operation of each of thes units are:

1. For the plant in part (a) of Fig. 8.6, a change in flow patter from parallel to series operation of the upflow units should be made and small quantities of Ca(OH)2 or CaCl2 should be added to th plant flow emerging from the primary upflow unit.

MIX

Fig. 8.6-Representative flow diagrams for lime-soda softening plants.

Fig. 8.7-Representative flow diagram for excess-lime softening plants. TABLE 8.13-REMOVAL OF STRONTIUM: PILOT-PLANT AND JAR-TES

recirculated from the settling tank to the mixing basin, and sn quantities of Ca(OH)2 or CaCl, should be added to the flocculat basin.

3. For the plant in part (a) of Fig. 8.7, preformed solids should added to the recarbonation basin, the CO2 feed should be adjus to reduce pH levels to the desired values in the tank, small quanti of lime water should be added, and provision should be made for a tation in the basin to keep preformed solids from settling. Co pressed air should prove satisfactory for mixing plant flow with added lime water and for preventing the preformed solids fr settling.

4. For the plant in part (b) of Fig. 8.7, preformed solids should recirculated from the settling tanks to the heads of the flocculati basins, and small quantities of Ca(OH)2 or CaCl2 should be add to these basins. In addition, if the recarbonation basin is to be us for strontium removal, all modifications required for the plant illu trated in part (a) of Fig. 8.7 must be made.

Lacy 28 evaluated the efficiency of a full-scale Spaulding upfil precipitator-clarifier (Erdlator Solids-contact Clarifier, Fig. 8.8 His results, which show removals for various radionuclides a mixtures of radionuclides ranging from 46 to 93%, are summariz in Table 8.14.

8-1.8 lon-exchange Systems

Commercial size (1.8 cu ft) ion-exchange systems were evaluat by Lacy 28 at ORNL; his results are summarized in Table 8.15. F the mixed wastes studied, cation-exchange resins on the Na+ cyc were less effective than those on the H+ cycle (67 to 70% as compare to 82 to 89% removal, respectively). However, the volume of liqui fed through the units was much greater in the case of the resins o the Na+ cycle than for the resins on the H+ cycle. Where a mixed bed resin was used, a removal of 98 to 99% was indicated, but th throughput was reduced to 1500 gal.

8-1.9 Small-scale Commerical Units

Two types of commercial water-purification units were evaluate with respect to their effectiveness in removing radioactive component from a solution of fission products. In all, 12 units were tested, eac of which contained 36 g of a mixture of diatomaceous earth an activated carbon, 22 g of Nalcite SAR resin, and 22 g of Nalcite HC resin; 9 of the 12 units contained, in addition, 42 g of powdered iron The solution used in these studies had an activity of approximatel 10,000 counts/(min) (ml) (10% geometry) and had the following percentage composition: strontium-yttrium, 27.6; cerium-prase

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TABLE 8.15-ION-EXCHANGE REMOVAL OF RADIOACTIVITY FROM WATER CONTAINING MIXED FISSION

*Units 1.8 cu ft.