Behavior of Radium and Barium in a System Including Uranium Mine Waste Waters and Adjacent Surface Waters Ferdinand Sebesta, Petr Bene&* Josef SedlaEek, Jan John, and Roman Sandrik Department of Nuclear Chemistry, Technical University of Prague, 115 19 Prague 1, BBehova 7,Czechoslovakia
The effect of a large-scale purification of uranium mine waste waters using ion-exchange resins or precipitation of barium sulfate on the concentration of dissolved and particulate forms of radium and barium has been studied. The results indicated a variable efficiency of the purification, mainly due to an uneven function of ion exchangers or to an insufficient sedimentation of barium sulfate. The main factors regulating the concentration and the forms of radium and barium in adjacent surface waters were the dilution of waste waters with river water and the sedimentation of the particulate forms in the river. A close analogy has been observed between the behavior of radium and barium throughout the system. The distribution of both of the elements between the water phase and suspended solids obeyed the homogeneous distribution law for isomorphous coprecipitation of radium with barium sulfate. Consequently, the predominant particulate form of radium and barium in such waters was Ba(Ra)SOs. Discharge of waste waters from umnium mines in surface waters has long been a matter of concern due to possible environmental effects of radioelements and heavy metals contained in such waters. Radium and barium belong to the most dangerous elements from this point of view because of their large content in uranium mine effluents (barium is often added during purification of mine waters) and because of their toxicity to man. Very few interpreted data have been published on the forms of existence and behavior of these two trace elements in the systems including mine effluents and adjacent surface waters. Tsivoglou et al. ( I ) studied the migration of radium in the Colorado River basin and found that a great part of the dissolved radium had gone into solution from river-bottom sediments. Just9n and StanBk (2) analyzed the effect of dilution of uranium mine effluents with river water on the concentration of radium downstream from the effluent discharge at several localities in Czechoslovakia and claim that a correction coefficient ranging from 1.2 to 2.5 must be used when calculating the radium concentration by using the common mixing rule. They found a positive correlation between radium concentration and concentration of sulfates or calcium in the river waters contaminated with mine effluents. Iyengar and Markose (3) reported seasonal variations of radium concentration in an Indian river contaminated with waters from a uranium mill tailings pond, which were main!y due to the dilution effect during the monsoon period. Hanslik and Mansfeld ( 4 ) studied contamination of a small Czech river by dissolved and particulate radium from purified mine effluents. They observed a significant increase in the concentration of radium during high water flow, which they explained by a raising of river-bottom sediments. The flow rate influenced also the ratio of dissolved to particulate forms of radium in river water. In this paper a typical water system has been chosen, and migration of radium and barium has been studied in order to elucidate the principal factors that regulate the fate of radium released with mine waters and of barium added to such waters. An attempt has been made to explain the observed behavior in terms of common physicochemical principles. 0013-936X/81/0915-0071$01.00/0 @ 1981 American Chemical Society
Investigated Water System Figure 1 presents a schematic layout of the water system investigated, indicating also purification methods and the location of places where samples of water were regularly taken for analyses. Surface waters in the studied locality are contaminated with radium mainly from two sources of waste waters: drilling and mining waters, both containing considerable amounts of natural radionuclides. Drilling waters are waters pumped out from relief boreholes around the mine. These waters contain only a small amount of suspended solids, and most of their radium is in dissolved form. Mining waters are pumped directly from the mine. Their content of suspended solids is higher, and a significant part of the radium is present in particulate forms. Further data on both of the waters are given below as determined at sampling places 1and 3. As shown in Figure 1,two different methods of purification are employed in the studied system. Drilling waters are purified by using cation-exchange resins in a fluid bed arrangement (spiractors). The effluents from spiractors are led directly to the receiving system of surface waters (via a small brook) and partially mixed with mining waters and led to a sedimentation pond. The sampling was done a t the inlet (1) and the outlet (2) of the spiractors in order to enable direct analysis of the purification effect. Purification of mining waters is done by precipitation of barium sulfate. Solutions of barium chloride and sodium sulfate are dosed into the waters in a molar ratio of 1:2. During our samplings, the average amounts added corresponded to -12 mg of BaClz and 18 mg of NaZS04 per liter of mining water. The waters are led to a sedimentation pond through a piping system 800 m long. The residence time of water in the piping is 8 min. The residence time in the sedimentation pond varies according to the effluent flow rate and to other conditions, but it was at least 2 h during our measurements. Our sampling places were situated before the precipitation (3), at the end of the piping system (4),and a t the outlet of the sedimentation pond ( 5 ) (see Figure 1). Effluent from the sedimentation pond flows through a waste-water channel -5 km long to a small river (the mean annual flow rate, 0.99 m3/s, at sampling place 9). Four additional sampling places were located as follows: on the wastewater channel, 500 m upstream from its confluence with the river (6),on the river, -800 m upstream of the confluence (9), 1000 m downstream of the confluence ( 7 ) , and 12 km further downriver (8). Samplings and Analyses Water samples collected in two 10-L polythene bottles were filtered through a Synpor 6 membrane filter 90 mm in diameter (Synthesia, UhiinBves, mean size of pores 0.4 pm) within 2 h after the sampling. The filtrate was immediately acidified with 10 mL of concentrated hydrochloric acid per liter, and transported or stored before analysis in closed polythene bottles. The filter with retained solids was stored in a petri dish before the analysis. The amount of retained solids was determined by weighing after drying the filter at room temperature. The p H values of water samples were measured in Volume 15, Number 1, January 1981
71
DRILLING WATER
MINING J'WATER
717T nuclear counter equipped with a light-tight sample changer (all Tesla, Czechoslovakia). For the evaluation of the absolute activity of 226Ra,the method of standard addition was used. Two aliquots were taken for analysis from each sample: one as received, the second one with an exactly known amount of standard radium solution added. The original radium content was calculated from the radioactivities of both of the aliquots, treated in exactly the same way. As the waters contained also 224Raand 223Ra,the radioactivity of 226Rawas measured 4-5 weeks after the treatment of samples. The method enabled us to determine radium down to -0.5 pg with the precision characterized by a standard deviation of a single determination of 15%in the range of 5-30 pg. The same method was employed for the determination of particulate forms of radium retained on filters. In this case, however, the filter with the retained solids was first washed with 500 mL of a hot (>90 "C) solution of a 0.1 M disodium salt of EDTA in 1.7 M NHdOH, and the filter with the residue was dissolved by evaporating it successively with concentrated HN03, concentrated H N 0 3 HzO2 (l:l),concentrated HF, concentrated HN03, and concentrated H N 0 3 HC1 (1:l). The amount of particulate forms of radium is the sum of radium found in the eluate and in the dissolved residue. Barium in acidified filtrates was determined by atomic absorption spectrophotometry after preconcentration of barium on strongly acidic cation-exchange resin (7). The Model 306 Perkin-Elmer atomic absorption spectrophotometer with an acetylene-air flame was used for the determination. Particulate barium was determined by this method without the preconcentration in the solutions obtained by the washing of the filters with retained solids (see above). It was proved that more than 95%of the barium was eluted from the filter. Concentration of sulfates in acidified filtrates was determined gravimetrically as Bas04 ( 5 ) .
CREEK WASTE WATER CHANNEL
Flgure 1. Schematic picture of the water scale).
system studied (not to
the laboratory by using a PHM 52 pH meter and a G202C glass electrode (Radiometer, Copenhagen). In order to assess the possible extent of adsorption of radium on the membrane filters used, we studied the adsorption from preliminary filtered mine effluents. The filtered effluents containing -1000 pg of 22sRa per liter were labeled with 224RaC1zand slowly filtered through the membrane filter. The filter was then washed with water and dissolved in hot concentrated nitric acid. The adsorption was evaluated from the radioactivity of z24Rain the resulting solution. It has been found that only 0.2% of the radium was adsorbed, which was negligible as compared to the error of radium determination. A similar conclusion can be drawn about the adsorption of barium on the filter, since the physicochemical behavior of radium and barium is known to be analogous. Moreover, the concentration of barium in studied waters was by several orders of magnitude higher than the concentration of radium so that its relative adsorption loss should have been even lower. The radium in acidified filtrates was determined by measuring the a activity of 226Raseparated by coprecipitation with barium-lead sulfate and mixed in the form of Ba(Ra)S04 with luminophore (5,6).The measurements were carried out with an NNC 211 bare photomultiplier tube using an NZQ
+
+
Behavior of Radium and Barium during Purification of Waste Waters The results obtained by analyses carried out on samples from sampling places 1-5 are shown in Table I. Minimum, maximum, and mean values are presented for samples taken
Table 1. Results of Water Analyses sampling place no. value
water temp (OC) water pH suspended solids (mg/L) dissolved Ra (pg/L) particulate Ra (pg/L) dissolved Ra ( % ) dissolved Ba (%) dissolved Ba (mg/L) particulate Ba (mg/L) dissolved sulfate (mg/L) -log K,, (BaS04) sampling place no. value
water temp ( O C ) water pH suspended solids (mg/L) dissolved Ra (pg/L) particulate Ra (pg/L) dissolved Ra ( % ) dissolved Ba (%) dissolved Ba (mg/L) particulate Ba (mg/L) dissolved sulfate (mg/L) -log k,, (BaS04)
72
1 min
10.5 6.33 3 265 1.6 97 92 0.08 92 0.18 f 0.05 4-C1BP > 3-ClBP. The total observed range in these relative rates was only a factor of 3.7. The turnover time of monochlorobiphenyls in an Alaskan estuary is estimated to be on the order of 1 yr a t a concentration of 0.1 pg/L or less with longer turnover times probable a t higher concentrations. No significant buildup of partially degraded products was observed. 0013-936X/81/0915-0075$01.00/0
@ 1981 American Chemical Society
The polychlorinated biphenyls (PCBs) are now generally recognized as one of the most ubiquitous and persistent types of environmental contaminapts. These synthetic mixtures of chlorinated derivatives of biphenyl have found widespread industrial use due to their physical and chemical stability and their dielectric properties. Inadequate waste disposal procedures have led to their release into the environment where they have been routinely detected in soil, water, and biota. Environmental concern about PCBs centers on their toxic effects toward a wide range of organisms ( I ) and their modulating effects on microbial species composition (2,3). Volume 15, Number 1, January 1981 75
