Silica reduces the toxicity of aluminium to a tropical freshwater fish (Mogurnda mogurnda)

The toxicity of aluminium (Al) to fish in acidic waters has been well documented. It was therefore expected that Al toxicity would be significant in fish communities in Gadjarrigamarndah (Gadji) Creek, a seasonally flowing stream in tropical northern Australia. This creek receives acidic groundwater containing elevated concentrations of Al from earlier land irrigation of treated mine tailings water from the former Nabarlek uranium mine. It was hypothesised that Al toxicity was reduced by high levels of silica (Si) in the water, and the subsequent formation of Al-silicate complexes. This prompted a laboratory assessment of the toxicity of Gadji Creek water to sac-fry of the native fish, Mogurnda mogurnda, followed by more detailed investigation of the toxicity of Al and the influence of Si in reducing Al toxicity. No mortality of M. mogurnda sac-fry was observed in two toxicity tests using Gadji Creek water collected in August 1997 and September 1998. The majority of Al (80-95%) was calculated to be complexed with humic substances and sulfate, with < 1% being complexed with silicate. Assessment of the influence of silica on the acute toxicity of Al in the absence of natural organic complexants (i.e. in reconstituted freshwater, pH 5) revealed that Si reduced Al toxicity. As the molar ratio of Si:Al was increased, the percent survival of M. mogurnda sac-fry increased until there was no significant (P > 0.05) difference from the controls. However, speciation modelling again predicted that little (< 3%) Al complexed with silicate, with the speciation and bioavailability of Al remaining constant as the molar ratio of Si:Al increased. Therefore, the original hypothesis that Al-silicate complexes in solution reduced the toxicity of Al to M. mogurnda could not be supported. This potential mechanism, and an alternative hypothesis, that Si competes with Al for binding sites at the fish gill surface, requires further investigation.     

Kinetics of heat-assisted persulfate oxidation of methyl tert-butyl ether (MTBE)

The kinetics of heat-assisted persulfate oxidation of methyl tert-butyl ether (MTBE) in aqueous solutions at various pH, temperature, oxidant concentration and ionic strength levels was studied. The MTBE degradation was found to follow a pseudo-first-order decay model. The pseudo-first-order rate constants of MTBE degradation by persulfate (31.5 mM) at pH 7.0 and ionic strength 0.11 M are approximately 0.13 x 10(-4), 0.48 x 10(-4), 2.4 x 10(-4) and 5.8 x 10(-4) S(-1) at 20, 30, 40 and 50 degrees C, respectively. Under the above reaction conditions, the reaction has an activation energy of 24.5 +/- 1.6 kcal/ mol and is influenced by temperature, oxidant concentration, pH and ionic strength. Raising the reaction temperature and persulfate concentration may significantly accelerate the MTBE degradation. However, increasing both pH (over the range of 2.5-11) and ionic strength (over the range of 0.11-0.53 M) will decrease the reaction rate. Reaction intermediates including tert-butyl formate, tert-butyl alcohol, acetone and methyl acetate were observed. These intermediate compounds were also degraded by persulfate under the experimental conditions. Additionally, MTBE degradation by persulfate in a groundwater was much slower than in phosphate-buffer solutions, most likely due to the presence of bicarbonate ions (radical scavengers) in the groundwater.     

Toxicity of acid aluminium-rich water to seven freshwater fish species: a comparative laboratory study

The present study focuses on the relative sensitivity among freshwater fish species to aqueous aluminium. Seven common Scandinavian fish species were exposed to acidic Al-rich water, acidic Al-poor water, and approximately neutral water as a control. The relative sensitivity among the species to an acute aluminium challenge was documented, and was in the following order: Atlantic salmon, Salmo salar, as the most sensitive; then roach, Rutilus rutilus; minnow, Phoxinus phoxinus; perch, Perca fluviatilis; grayling, Thymallus thymallus; brown trout, Salmo trutta; and Arctic char, Salvelinus alpinus. Substantial mortality was observed in all species when exposed to the Al-rich medium. Some mortality was also observed in minnow, roach, and brown trout exposed to the acidic Al-poor medium and the control medium. A high resistance to aluminium was observed in Arctic char, while perch was found to be more sensitive to aluminium than expected and, for the first time, a toxic response to aqueous aluminium in grayling was documented. Through controlled experimental studies, the results confirm that aluminium is an important factor in the toxicity of acidified waters to freshwater fish species.     

Bioaccumulation of aluminium in the freshwater snail Lymnaea stagnalis at neutral pH

This study examined the accumulation of aluminium (Al) by the freshwater snail Lymnaea stagnalis at neutral pH, when most Al would be predicted to be in an insoluble form (Al(OH)(3)). Snails were exposed to a range of Al concentrations (38-285 microg l(-1)) for 30 days, followed by 20 days in clean water. Aluminium was measured using atomic absorption spectroscopy. Significant accumulation of Al occurred in the whole soft tissues, gut, digestive gland and kidney at the latest by day 10. High concentration factors were observed, ranging from 4.5 x 10(3) in the whole soft tissues to 6.3 x 10(4) in the kidney, corresponding to actual concentrations of 800 to 7500 microg g(-1), respectively. Proportionality between environmental (water) and tissue concentrations of Al was observed in the gut but not in the other tissues. Following transfer to clean water, rapid loss of Al from the whole soft tissues and gut was seen over the first 10 days. Loss of Al from the digestive gland was much less as a proportion of the total, with approximately 90% of the Al remaining in the tissue. In contrast, significant loss of Al from the kidney occurred between days 20 and 30, even in the continued presence of Al; little further loss occurred following transfer to clean water. Aluminium is clearly available to the snail at neutral pH, the most likely route of entry being the gut. This could facilitate entry of the metal into the food chain. The possible roles of the digestive gland and kidney in the handling of Al are discussed.     

Kinetics and mechanism of nitrite oxidation by hypochlorous acid in the aqueous phase

The rate coefficient for the reaction of nitrite with hypochlorite and hypochlorous acid has been studied using spectrophotometric measurements. The reaction rate has been determined in a wide range of H(+) concentration (5< or =-log[H(+)]< or =11). The kinetics were carried out as a function of NO(2)(-), H(+) and total hypochlorite ([HOCl](total)=[HOCl]+[ClO(-)]+[ClNO(2)]) concentrations. The observed overall rate law is described by: -d[HClO](T)dt=[a[NO(2)(-)](2)+b[NO(2)(-)]][H(+)](2)c+d[H(+)]+e[NO(2)(-)][H(+)](2)[HOCl](total)At T=298 K and in Na(2)SO(4) at an ionic strength (I=1.00 M), we obtained using a nonlinear fitting procedure: a=(1.83+/-0.36)x10(7) s(-1), b=(1.14+/-0.23)x10(5) Ms(-1), c=(1.12+/-0.17)x10(-13) M, d=(1.43+/-0.29)x10(-6) M(2) and e=(1.41+/-0.28)x10(3) M where the errors represent 2sigma. According to the overall rate law, a/b=k(1)/k(3), b/e=k(3), c=K(w), d/c=K(a), d=K(a)K(w) and e=K(1)K(a). In Na(2)SO(4) at an ionic strength (I=1.00 M), the values of K(1) and K(a) are (1.1+/-0.1)x10(-4) and 1.28x10(7) M(-1), respectively. A mechanism is proposed for the NO(2)(-) oxidation which involves the reversible initial step: NO(2)(-)+HOCl left harpoon over right harpoon ClNO(2)+OH(-) (K(1)), while ClNO(2) undergoes the two parallel reactions: attack by NO(2)(-) (k(1)) and hydrolysis (k(3)). ClNO(2) and N(2)O(4) are proposed as important intermediates as they control the mechanism. The rate coefficients k(1) and k(3) have been determined at different ionic strengths in NaCl and Na(2)SO(4). The influence of the ionic strength and ionic environment has been studied in this work.     

The influence of plantation forestry on the pH and aluminium concentration of upland welsh streams: a re-examination

Previous studies relating forest presence to stream acidity and aluminium concentration were based on small numbers of catchments, often precluding the elimination of confounding influences on stream chemistry, such as geology or soil type. Spatial patterns in aluminium and pH data from 113 Welsh catchments of contrasting land use were therefore analysed in three different ranges of acid sensitivity (< 10, 10-15, 15-25 mg CaCO(3) litre(-1) total hardness). In each range, pH declined and aluminium increased significantly with increasing percentage forest cover. There was no evidence that the relationships reflected a spurious effect of forest location. Where aluminium concentrations were elevated under forest in a sub-set of 13 streams, aluminium was present predominantly in the labile form, most toxic to fish. Regressions of pH and aluminium on percentage forest cover provide a useful method of assessing the amount of forest in Welsh catchments which might give rise to given chemical conditions (e.g. pH <6, Al > 80 microg litre(-1)), though some difficulties are likely in accurately specifying the conditions desirable for fish or other biota.     

Changes in gill morphology of Atlantic salmon (Salmo salar) smolts due to addition of acid and aluminum to stream water

One-year-old Atlantic salmon smolts were held in three artificial channels adjacent to a softwater (mean sp. cond. 30 microS cm(-1), circumneutral stream. Water in one channel was untreated (mean pH 6.25); the others received additions of acid (to mean pH 5.6), or acid plus aluminum (to mean pH 5.5; mean exchangeable Al 158 microg litre(-1)). Gills were sampled after 16 and 23 days of exposure for morphometric examination. On primary lamellae, chloride cells were more numerous in both experimental treatments than in controls. In contrast, numbers of chloride cells on secondary lamellae were elevated only in fish exposed to acid without added Al. Chloride cell size and shape also varied with time and treatment. Fewer gill mucous cells were found in fish exposed to acid plus Al than in controls. Chloride cell proliferation and structural changes may represent an attempt to compensate for increased ionic effluxes with low pH stress by increasing uptake. However, if Al concentrations are high, chloride cells do not proliferate along the secondary lamellae, or proliferating cells are damaged and lost. This may limit the potential to increase ionic uptake.     

Accumulation of aluminium by the freshwater crustacean Asellus aquaticus in neutral water

This study examined the accumulation of aluminium (Al), mostly as the insoluble (Al(OH)(3)) species, by the freshwater crustacean Asellus aquaticus at neutral pH. Animals were exposed to a range of Al concentrations (5-356 microg l(-1)) in three experiments. The first two were of 30 and 50 days duration, respectively, followed by transfer of the A. aquaticus to water containing no Al for 20 days. The third used live and dead animals in order to investigate the contribution made by surface adsorption of Al to the total accumulated. Significant accumulation of Al in the whole tissues occurred by day 10 in all animals in the 30- and 50- day experiment. Peak concentrations of Al were measured in animals between days 10 and 20 with high concentration factors ranging from 1.4 x 10(4) to 5.5 x 10(3). By day 30, accumulated Al had fallen but was still significantly greater than the control in the 50- day exposure experiment. This 30- day increase followed by decreased accumulation of Al was repeated over the remaining exposure period (i.e. 30-50 days) although rates of uptake and loss and peak tissue levels of Al were higher. Proportionality between environmental (water) and tissue concentrations of Al occurred at day 20 but not at day 45. Significantly more Al was accumulated by dead animals than live animals at all Al exposure concentrations. These results suggest that Al is available to the crustacean at neutral pH and that the cuticle may provide an important site of uptake.     

Experimental and modeling studies on sorption and diffusion of radium in bentonite

The sorption and desorption behavior of radium on bentonite and purified smectite was investigated as a function of pH, ionic strength and liquid to solid ratio by batch experiments. The distribution coefficients (Kd) were in the range of 10(2) to > 10(4) ml g-1 and depended on ionic strength and pH. Most of sorbed Ra was desorbed by 1 M KCl. The results for purified smectite indicated that Ra sorption is dominated by ion exchange at layer sites of smectite, and surface complexation at edge sites may increase Ra sorption at higher pH region. Reaction parameters between Ra and smectite were determined based on an interaction model between smectite and groundwater. The reaction parameters were then used to explain the results of bentonite by considering dissolution and precipitation of minerals and soluble impurities. The dependencies of experimental Kd values on pH, ionic strength and liquid to solid ratio were qualitatively explained by the model. The modeling result for bentonite indicated that sorption of Ra on bentonite is dominated by ion exchange with smectite. The observed pH dependency was caused by changes of Ca concentration arising from dissolution and precipitation of calcite. Diffusion behavior of Ra in bentonite was also investigated as a function of dry density and ionic strength. The apparent diffusion coefficients (Da) obtained in compacted bentonite were in the range of 1.1 x 10(-11) to 2.2 x 10(-12) m2 s-1 and decreased with increasing in dry density and ionic strength. The Kd values obtained by measured effective diffusion coefficient (De) and modeled De were consistent with those by the sorption model in a deviation within one order of magnitude.     

Effects of clearfelling on stream and soil water aluminium chemistry in three UK forests

Data are presented demonstrating how clearfelling has changed soil and stream water aluminium chemistry. For soil waters, a strong empirical relationship was observed between inorganic aluminium (Al(inorg)) and total inorganic anion (TIA) concentrations. Before felling, chloride and sulphate accounted for the largest proportion of the TIA concentration. After felling, in soils where nitrification was active, nitrate became increasingly important. Where this led to an increase in TIA, Al(inorg) concentrations increased. Over five years, nitrate concentrations have fallen, along with TIA, resulting in a sympathetic decline in Al(inorg). Streams draining clearfelled areas initially became more acid, although chloride and sulphate concentrations decreased. Stream water nitrate concentrations increased soon after felling and remained higher than controls for up to four years. While nitrate concentrations were high, Al(inorg) remained unchanged. Subsequently, as nitrate and TIA decreased, Al(inorg) also declined to concentrations below those in the control stream. Clearfelling upland forests will not necessarily result in immediate improvements in water quality, although long-term benefits may be seen before canopy-closure of the next crop.     

A laser flash photolysis study of the decay of SO4- and Cl2- radical anions in the presence of Cl- in aqueous solutions

The rate constant for the reaction of sulphate radical (SO4-) with Cl- has been determined using laser photolysis, at 248 nm, of peroxodisulphate anions to produce the radicals and time resolved optical absorption of the transient species (at 450 or 480 nm for SO4- and 350 nm for Cl2-) for the kinetic determinations. The experiments were performed, in the absence of added sulphate, as a function of temperature and ionic strength and yielded (at an ionic strength of 0.0157 M): kIV = (9.90+/-0.16) x 10(9) exp((-7.12+/-2.0) kJ mol(-1)/RT) M(-1) s(-1), where the errors reflect the 2sigma statistical error. This reaction produces Cl2-, the formation and decay of which were also monitored allowing a determination of the rate constant of its second-order self-recombination reaction which gave k = (6.50+/-1.40) x 10(8) M(-1) s(-1) at 293 K and zero ionic strength.     

Effects of ionic strength on the production of short chain volatile hydrocarbons by Dunaliella salina (Teodoresco)

The effect of ionic strength on the production of short chain volatile hydrocarbons was studied in cultures of Dunaliella salina. Axenic cultures of D. salina were grown at three different ionic strengths 0.5, 2 and 3 M of NaCl in Johnson (J/1) culture medium [Journal of Bacteriology 95 (1968) 1461] under the following laboratory growth conditions: a 12:12 h photoperiod, 300 micromolm(-2)s(-1) of photosynthetic active radiation (PAR) provided by a fluorescent lamp of 40 W combined with a 100 W incandescent lamp at 20 +/- 1 degrees C at pH 7.5. C1 to C5 hydrocarbons were detected using a head space technique and GC-FID. Cell numbers and growth rate was greatest at 2 M NaCl 4.3 x 10(6) cellml(-1) after a 15 days period of culture. Maximum hydrocarbon production was measured in the concentration of 0.5 NaCl with lower production rates in the more concentrated solutions. The principal hydrocarbon was pentane at 0.5 M but was ethane in 2 and 3 M solutions. Production rates for individual compounds ranged between 0.13 and 22 x 10(-15) microgCcell(-1)h(-1). It is suggested that the ability to produce and release volatile organic compounds of D. salina is related to osmotic conditions established by the ionic strength of growth solution.     

Influence of trivalent electrolytes on the humic colloid-borne transport of contaminant metals: competition and flocculation effects

With the objective to assess the relevance of competitive effects in respect of the humic colloid-borne migration of actinides in case of release, the influence of Al(III) on humate complexation of La(III) as an analogue of trivalent actinides was investigated for various humic materials by using 140La as a radioactive tracer, allowing measurements in very dilute systems to simulate realistic settings. Generally, competition by aluminium is not detectable unless the metal-loading capacity of the humic colloids is nearly exhausted. For average contents of organic carbon, a threshold value of 10(-6) M Al(III) can be specified. The metal exchange turned out to be kinetically hindered. Effects on co-adsorption of La(III) and humic acid were found to be less important. Immobilization by the concomitantly induced flocculation process outweighs the role of displacement effects. Comparative studies on complexation and flocculation of humic acid with Al(III), Ga(III), In(III), Sc(III), Y(III), and La(III) were undertaken in order to evaluate the influence of specific properties apart from ion charge and to characterize the mechanism of flocculation. In spite of considerable variations in the binding affinities among these metals, it can be inferred that the possibility of significant competitive effects in natural aquatic systems is confined to Al(III). Complex stabilities and flocculation efficiencies proved to be interrelated. Precipitation is thus attributed to homocoagulation of humic colloids induced by charge compensation, which is further supported by flocculation experiments with Al(III) depending on pH, ionic strength, and humic acid concentration.     

Influence of some additives to aluminium species distribution in aluminium coagulants

Aluminium ions hydrolyse and polymerise into different species in water. Main aluminium species in aluminium coagulant solutions are monomeric Al species (Al1) and polymeric Al species Al13O4(OH)24(7+) (Al13). The aluminium species distribution in coagulant solutions can be influenced by many parameters. This paper studies influences of concentrations of total aluminium species (Al(t)) and other species--OH-, polysilicic acid and ferric species, which were added in aluminium coagulant solutions, on the aluminium species distribution through 27Al nuclear magnetic resonance (NMR) analysis. Results show that only Al1 and no Al13 exist in coagulant solutions at higher Al(t) concentrations (over 1 mol l(-1)), while both species exist at lower Al(t) concentrations (0.1 mol l(-1)). The increase of OH/Al value (molar ratio) increases the concentration of Al13 in coagulant solutions, while the addition of polysilicic acid and ferric species decreases the concentration of Al13.     

Homogeneous degradation of 1,2,9,10-tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light

The homogeneous degradation of the polychlorinated n-alkane, 1,2,9,10-tetrachlorodecane (T4C10), was studied in aqueous solutions of hydrogen peroxide, including Fenton and photo-Fenton reaction conditions. All solutions were adjusted to a pH of 2.8 and an ionic strength of 0.1 M NaClO4 prior to photolysis. T4C10 (2 x 10(-6) M) was substantially degraded by the H2O2/UV system (1.0 x 10(-2) M H2O2), with 60% disappearance in 20 min of irradiation in a photoreactor equipped with 300 nm lamps of light intensity 3.6 x 10(-5) Ein L(-1) min(-1) (established by ferrioxalate actinometry). The reaction produced stoichiometric amounts of chloride ion indicating complete dechlorination of the chlorinated n-alkane. T4C10 degraded very slowly under Fenton (Fe2+/H2O2/dark) and Fenton-like (Fe3+/H2O2/dark) conditions. However, when the same solutions were irradiated, T4C10 degraded more rapidly than in the H2O2/UV system, with 61% disappearance in 10 min of exposure. The rapid degradation is related to the enhanced degradation of hydrogen peroxide to oxidizing *OH radicals under photo-Fenton conditions. Degradation was inhibited in both the H2O2/UV and photo-Fenton systems by the addition of KI and tert-butyl alcohol due to *OH scavenging.     

Survival of brown trout during spring flood in DOC-rich streams in northern Sweden: the effect of present acid deposition and modelled pre-industrial water quality

Mortality and physiological responses in brown trout (Salmo trutta) were studied during spring snow melt in six streams in northern Sweden that differed in concentrations of dissolved organic carbon (DOC) and pH declines. Data from these streams were used to create an empirical model for predicting fish responses (mortality and physiological disturbances) in DOC-rich streams using readily accessible water chemistry parameters. The results suggest that fish in these systems can tolerate higher acidity and inorganic aluminium levels than fish in low DOC streams. But even with the relatively low contemporary deposition load, anthropogenic deposition can cause fish mortality in the most acid-sensitive surface waters in northern Sweden during spring flood. However, the results suggests that it is only in streams with high levels of organically complexed aluminium in combination with a natural pH decline to below 5.0 during the spring where current sulphur deposition can cause irreversible damage to brown trout in the region. This study support earlier studies suggesting that DOC has an ameliorating effect on physiological disturbances in humic waters but the study also shows that surviving fish recover physiologically when the water quality returns to less toxic conditions following a toxic high flow period. The physiological response under natural, pre-industrial conditions was also estimated.     

Effects of aluminium in acid streams on growth and sporulation of aquatic hyphomycetes

We investigated, by field and laboratory experiments, the effects of aluminium in an acid stream (pH 5.0) on the growth and sporulation of aquatic hyphomycete fungi which degrade organic litter. The stream water had monomeric aluminium (Al(m)) concentrations of 9.1-13.4 microm - fifty times higher than a nearby circumneutral stream. Alder leaves submersed in the stream accumulated Al, most of which was tightly bound. Growth rates of four species of aquatic hyphomycetes were altered by inclusion of Al(m) in the culture medium. On a polypectate substrate, and on low-phosphate medium with glucose, growth rates increased significantly. On a low-nutrient substrate of homogenized alder leaves, growth rates were inhibited by aluminium. The pattern of mycelial growth was found to be different on a polypectate medium including Al(m), compared with a control without aluminium. There was a significant increase in hyphal radial growth and a decrease in the hyphal growth unit. The effect resembled the growth of a starved fungal colony. Treatment with Al(m) decreased pectinase production by the four fungal species tested. The capacity of these species to sporulate was reduced by flooding culture plates with Al(m) solution. These deleterious metabolic effects were most severe in isolates taken from circumneutral streams and less marked, though significant, in species originating from acid streams.     

Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the vadose zone

To investigate the coupled effects of solution chemistry and hydrodynamics on the mobility of quantum dot (QD) nanoparticles in the vadose zone, laboratory scale transport experiments involving single and/or sequential infiltrations of QDs in unsaturated and saturated porous media, and computations of total interaction and capillary potential energies were performed. As ionic strength increased, QD retention in the unsaturated porous media increased; however, this retention was significantly suppressed in the presence of a non-ionic surfactant in the infiltration suspensions as indicated by surfactant enhanced transport of QDs. In the vadose zone, the non-ionic surfactant limited the formation of QD aggregates, enhanced QD mobility and transport, and lowered the solution surface tension, which resulted in a decrease in capillary forces that not only led to a reduction in the removal of QDs, but also impacted the vadose zone flow processes. When chemical transport conditions were favorable (ionic strength of 5 × 10(-4)M and 5 × 10(-3)M, or ionic strengths of 5 × 10(-2)M and 0.5M with surfactant), the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were meso-scale processes, where infiltration by preferential flow results in the rapid transport of QDs. When chemical transport conditions were unfavorable (ionic strength of 5 × 10(-2)M and 0.5M) the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were pore-scale processes governed by gas-water interfaces (GWI) that impact the mobility of QDs. The addition of surfactant enhanced the transport of QDs both in favorable and unfavorable chemical transport conditions. The mobility and retention of QDs was controlled by interaction and capillary forces, with the latter being the most influential. GWI were found to be the dominant mechanism and site for QD removal compared with solid-water interfaces (SWI) and pore straining. Additionally, ripening phenomena were demonstrated to enhance QDs removal or retention in porous media and to be attenuated by the presence of surfactant.     

Abundance and population structure of perch (Perca fluviatilis L.) in some acidic Norwegian lakes

Abundance (catch per unit effort, n=3752) and population structure of perch Perca fluviatilis were studied in 30 acidic Norwegian lakes with relation to pH (4.3-5.9), calcium (0.41-2.44 mg litre(-1)), labile aluminium (24-255 microg litre(-1)) and total organic carbon (TOC, 1.7-13.8 mg C litre(-1)). Standard series of bottom gill-nets were used to sample fish populations. A multiple regression analysis showed that abundance was significantly correlated to TOC (P<0.05) and, to a smaller extent, to the Ca in lakes with concentrations between 0.41 and 1.70 mg litre(-1) (P=0.07). The lakes which were inhabited by pike were excluded from the analysis. Recruitment failure seems to be the main cause of reductions in perch numbers in the lakes studied. However, high mortality among adult individuals was also evident, and an episode of fish kill was observed in one of the lakes.     

Adsorptive separation of cadmium from aqueous solutions and wastewaters by riverbed sand

Application of riverbed sand for the adsorptive separation of cadmium(II) from aqueous solutions has been investigated. Removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5 x 10(-5) to 1.0 x 10(-5)M at pH 6.5, 25 degrees C temperature, agitation speed of 100 rpm, 100 microm particle size and 1.0 x 10(-2) NaClO4 ionic strength. Process of separation is governed by first order rate kinetics. The value of rate constant of adsorption, k(ad), was found to be 2.30 x 10(-2)per min at 25 degrees C. Values of coefficient of mass transfer, beta L, were calculated and its value at 25 degrees C was found to be 1.92 x 10(-2)cm/s. Values of Langmuir constant were calculated. Values of thermodynamic parameters delta G0, delta H0 and delta S0 were also calculated and were recorded as -0.81 kcal/mol, -9.31 kcal/mol and -28.10 cal/mol at 25 degrees C. pH has been found to affect the removal of cadmium significantly and maximum removal, 58.4%, has been found at pH 8.5. Process can be used for treatment of cadmium(II) rich wastewaters.