Patent Number: 045333955
Section: description

EXAMPLE 1 A prepared solution representing an evaporation concentrate (MAW-concentrate) in accordance with the data as given in FIG. 1 was introduced into a heatable mixing auger. The composition of the concentrate is given in Table 1. A flow of 150 l/h was maintained into which Portland cement 35F was metered at a rate of 24 kg/h. A process temperature of between 130.degree. and 180.degree. C. was maintained. A fixation mixture was produced at a rate of 30 l/h which included 30 kg/h of salts, 24 kg/h of cement and 6 kg/h of water. The fixation mixture was discharged from the mixing auger into a waste container in which it hardened. The solid end product contained 50 wt.% of salts and the water-cement number was 0.25. The steam escaping during mixing and evaporation amounted to 134 kg/h of condensate. TABLE 1 ______________________________________ COMPOSITION OF THE MAW CONCENTRATE Element or Compound Concentration in g/l ______________________________________ NaNO.sub.3 300 Al 0.23 Ca 1.5 Cr 0.08 Cu 0.15 Fe 0.38 K 0.08 Mg 0.75 Mn 0.08 Mo 0.38 Ni 0.08 Ru 0.15 Zr 0.15 Sodium oxalate 5 Sodium tartrate 5 EDTA 1 NaF 1 Tensid (Marlox FK 64) 1 Tensid (Marlophen 812) 1 Na.sub.2 HPO.sub.4 5 Sodium citrate 5 Tributylphosphate (TBP) 0.2 Dibutylphosphate (DBP) 0.2 Kerosene 0.02 ______________________________________ All elements were introduced in the form of nitrates with the exception of Mo which was used as sodium molybdate. During non-active tests, 10 g/l inactive Cs or, respectively, Sr were introduced. EXAMPLE 2 161 g Portland cement (PC 35F) were mixed in a retort with 354 g NaNO.sub.3 solution (NaNO.sub.3 content of 90 g). Such a mixture has a water-cement number of 1.64 and contains 17.5% by weight of salt. In place of Portland cement, blast furnace cement, trass cement or pozzuolona cement may be used. Volume reduction by mixing/evaporation at 130.degree.-180.degree. C. resulted in evaporation of 215 g H.sub.2 O. The fixation mixture with a water-cement number of 0.3 and a salt content of 30 wt.% was easily transferred from the retort into prismatic forms wherein it hardened. After 28 days storage time, the end products had dynamic elasticity-module values of 18-25 N/mm.sup.2 ; the crash resistance was 25-35 N/mm.sup.2. The mechanical resistance of those products with a high salt content and low water-cement number is, consequently, comparable to, or better than, that of products with a 10% (by weight) salt content and water-cement numbers of 0.4 to 0.45 as they are known in the art. Before evaporation and mixing, for example, 0.01 to 0.2 wt.%, of a known setting retardant or of a liquifier may be added to the mixture if an evaporation temperature at the lower end of the given range is selected, that is, if the mixing and evaporation period is relatively long. It is also possible to perform the mixing and evaporation step under vacuum so that the operating temperature is relatively low which is advantageous if premature setting must be avoided. The results of this example show that solid products of cement with a low water-cement number (0.3) and a relatively high waste content (30% by weight), which values exceed those of products made in accordance with the state of the art, can be made in a continuous process in which the mixture of cement and aqueous waste has originally a high water-cement number (&gt;1) but in which, during mixing, the water content is reduced, by evaporation, to the desired end value. With a continuous process, residence times of the mixture in the mixer-evaporator of about 5-10 minutes can be obtained without problems (for comparison: bitumination--3 minutes) so that, under the selected conditions, premature setting and solidification of the mixture can be avoided. Leach Resistancy Diffusion coefficient (m.sup.2 /s) for Co-137. TABLE 2 ______________________________________ Product Composition NaCl Solution Quinary Solution Water-Cement normal normal Number = 0.4 conditions) conditions) PC = Portland Cement (at RT) (at RT) ______________________________________ PC 35F + 10 wt. % NaNO.sub.3 8.1 .times. 10.sup.-3 8.5 .times. 10.sup.-14 PC 35F + 10 wt. % 1.2 .times. 10.sup.-13 1.5 .times. 10.sup.-14 NaNO.sub.3 +5 wt. % Bentonite PC 35F + 40 wt. % NaNO.sub.3 4.5 .times. 10.sup.-12 2.7 .times. 10.sup.-13 PC 35F + 40 wt. % 8.4 .times. 10.sup.-15 1.0 .times. 10.sup.-15 NaNO.sub.3 +5 wt. % Bentonite ______________________________________ The results show that the leach resistancy of products with or without addition of Bentonite is similar. Samples with a high salt content benefit by the addition of Bentonite since they show a lower Cs release. Corrosion Resistancy in Quinary Solution Changes in the attenuation of the resonance frequency, that is, changes in the dynamic elasticity module (which is calculated from the attenuation) and changes in the weight of the samples, are employed as a measurement for progress of corrosion. TABLE 3 ______________________________________ Sample weight (g) 10% Salt 45% Salt E-Module (N/mm.sup.2) Storage Time w/c = 0.4 w/c = 0.25 10% Salt 45% Salt ______________________________________ 0 days PC 35F 61.8 65.4 18.5 23.0 5 days 58.0 65.7 14.0 17.0 15 days 60.0 66.3 13.5 16.0 50 days 61.0 66.3 13.0 14.5 90 days 61.0 66.2 12.5 13.5 0 days BFC 35L 57.5 64.8 19.5 23.5 5 days 57.0 65.5 15.0 18.0 15 days 56.5 66.0 15.0 17.0 50 days 57.0 66.7 15.0 16.0 90 days 57.5 67.2 15.0 14.0 ______________________________________ w/c = watercement number (wt. ratio) PC = Portland cement BFC = blast furnace cement From the test results listed, it may be seen that samples of PC 35F exhibit no differences and samples of BFC 35L exhibit only small differences in corrosion resistancy for different salt contents. EXAMPLE 3 315 g of the concentrate (containing NaNO.sub.3) of Table 1 in Example 1 were mixed with 140 g Portland cement 35F (w/c=1.6) and heated in an oil bath of 140.degree. C., whereby 180 g H.sub.2 O were evaporated (in 4 hours). To the resulting viscous mixture 26 g of Na.sub.2 SiO.sub.3 .multidot.5H.sub.2 O was added and the mixture was then filled into prismatic forms. The samples showed the normal hardening progress. After 28 days hardening time, the dynamic E-module was comparable with that of products made in accordance with prior art methods. The composition of the solid end products was: ##EQU1## EXAMPLE 4 380 g of a borate-containing solution, according to borate-containing waste water of a pressurized water nuclear reactor (Table 4) were mixed with 175 g cement and subjected to an oil bath at a temperature of 140.degree. C. for 2 hours during which time 258 g H.sub.2 O was evaporated. The resulting flowable mixture was filled with prismatic forms wherein it exhibited a normal hardening progress. After 28 days, the dynamic E-module was 16 N/mm.sup.2. The composition of the solid end product was: ##EQU2## The method according to the invention presents a simple solution especially for the disposal of boric acid concentrates. It has been necessary so far, for the fixation of these concentrates, to adjust the pH value of 11-12 by additives (NaOH or Ca(OH).sub.2) in order to obtain a solid end product. However, these additives degraded the quality of the product. With the method according to the invention, solid fixation end products can be obtained without additives and these end products exhibit better quality and have a lower w/c number. TABLE 4 ______________________________________ CONCENTRATIONS IN g/l ______________________________________ NaOH 29 H.sub.3 BO.sub.3 180 Na.sub.2 SO.sub.4 30 Na.sub.2 HPO.sub.4 .times. 12H.sub.2 O 5 NaCl 5 Fe.sub.2 (SO.sub.4).sub.3 5 Cs.sub.2 SO.sub.4 10 Detergents (Hakar-Dekopur RS) 5 ______________________________________