Efficient arsenic depollution in water using modified maize powder

This article reports the synthesis of an efficient, low-cost material from maize powder to depollute arsenic-contaminated water. Arsenic is toxic for humans and other organisms even at low concentrations. The most well-known and severe case of arsenic poisoning through drinking water has been found in India and Bangladesh. Numerous inorganic materials have been tested for the removal of arsenic from water bodies over the last two decades. However, all such materials have several disadvantages such as unpredictable arsenic ion removal, high cost and the generation of toxic sludge that is often more difficult to manage. Alternatively, organic material from agricultural waste may be modified to enrich functional groups responsible for As sorption and, in turn, used to depollute contaminated waters. Here, Zea mays cob powder has been modified to remove arsenic species from water. Two modified materials were produced: an aminated maize powder and a thiolated maize powder. Amination was done using epichlorohydrin and dimethylamine. Thiolation was done using thioglycolic acids. Amination increased As (III) sorption from 70 to 75.8 % and As (V) sorption from 85 to 94.42 %, compared with unmodified maize powder. Thiolation increased As (III) sorption from 70 to 81.7 % and As (V) sorption from 85 to 90 %. Amination increased usability cycles from 3 to 5. Thiolation increased usability cycles from 3 to 6. The novel modified maize biosorbent has enough potential for the development of a low-cost technological pre-treatment step, prior to high-tech chemical treatments.     

砷浓度、形态及碳酸氢盐对蜈蚣草吸收砷的影响

为了探讨超富集植物蜈蚣草在处理高砷地下水方面的可行性,研究了水培条件下砷的浓度、形态和碳酸氢盐(HCO-3)对超富集植物蜈蚣草吸收砷的影响。实验中使用了浓度为0.1～100mg·L-1的As(III)和As(V)溶液。HCO-3处理中,HCO-3浓度范围为0.5～20mmol·L-1,As(III)或As(V)的浓度为5mg·L-1。结果表明,在水培条件下,蜈蚣草具有明显的耐高砷特征。当介质砷含量高达100mg·L-1时,砷的去除率可达到80%,且对As(III)的吸收效率高于As(V)。植物体内砷形态研究表明,蜈蚣草体内2种形态砷的含量与外源砷形态有一定的关系,As(V)处理条件下,植物体中的As(V)比例较As(III)处理高。高浓度的HCO-3(20mmol·L-1)处理对蜈蚣草地上部分生物量没有明显影响,但是抑制了地下部分的生长,并且对砷的吸收表现出明显的抑制作用。     

砷浓度、形态及碳酸氢盐对蜈蚣草吸收砷的影响

大同盆地是典型的高砷地下水分布区。利用从地方性砷中毒严重病区山阴县采集的高砷地下水样品,用稀释培养法实验研究了外加砷源对地下水中微生物数量的影响;同时基于生物学可培养法和16S rDNA序列比对法,选取代表性高砷水样,研究了耐砷菌的种群特征。结果表明,外加砷源对地下水中微生物数量影响显著,高浓度砷会抑制大部分微生物生长,使微生物数量减少;低浓度砷对微生物生长具有一定促进作用。通过多次分离、纯化从3个不同砷含量地下水样中分离到多株砷抗性菌,经鉴定属于主要为Bacillus、Pseudomonas、Paenibacillus、Aeromonas、Enterobacter5个属。从RDP(Ribosomal Database Project)分析显示3个水样可培养微生物组成不同,都有生存能力强能够耐低浓度NaAsO₂的Bacillales,优势耐砷菌是γ-proteobacteria,其中Enterbacter具有耐高浓度NaAsO₂的能力。     

Stabilization of the As-contaminated soil from the metal mining areas in Korea

The stabilization efficiencies of arsenic (As) in contaminated soil were evaluated using various additives such as limestone, steel mill slag, granular ferric hydroxide (GFH), and mine sludge collected from an acid mine drainage treatment system. The soil samples were collected from the Chungyang area, where abandoned Au–Ag mines are located. Toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, sequential extraction analysis, aqua regia digestion, cation exchange capacity, loss on ignition, and particle size distribution were conducted to assess the physical and chemical characteristics of highly arsenic-contaminated soils. The total concentrations of arsenic in the Chungyang area soil ranged up to 145 mg/kg. After the stabilization tests, the removal percentages of dissolved As(III) and As(V) were found to differ from the additives employed. Approximately 80 and 40% of the As(V) and As(III), respectively, were removed with the use of steel mill slag. The addition of limestone had a lesser effect on the removal of arsenic from solution. However, more than 99% of arsenic was removed from solution within 24 h when using GFH and mine sludge, with similar results observed when the contaminated soils were stabilized using GFH and mine sludge. These results suggested that GFH and mine sludge may play a significant role on the arsenic stabilization. Moreover, this result showed that mine sludge can be used as a suitable additive for the stabilization of arsenic.     

碳纳米管影响无机砷(As(III)和As(V))对大型蚤毒性的研究：特定砷形态的作用

作为一种新兴的纳米材料,羟基多壁碳纳米管(OH-MWCNTs)可能与其他污染物在水环境中共存,并进一步影响它们的毒性、输移和归趋。因此,评价碳纳米管存在下砷的毒性变化需要得到更多的关注。该试验探索了在不同pH值条件下,OH-MWCNTs诱导砷(As(III)和As(V))对水生生物大型蚤的毒性变化的潜在机制。发现了H₂AsO₃^-和H₂AsO₄^-是对大型蚤毒性最大的As(III)和As(V)。比较As(III)和As(V)的结果,发现pH值是影响砷毒性最重要的因素。此外,OH-MWCNTs影响砷对大型蚤毒性的结果表明,OH-MWCNTs的存在可以提高砷的毒性。通过吸附实验进一步研究了砷与OH-MWCNTs的相互作用。OH-MWCNTs 对As(V)吸附容量高于As(III)。总而言之, OH-MWCNTs对某些形态砷的吸附是解释砷毒性增强的可靠证据。
精选自Xinghao Wang, Ruijuan Qu, Ahmed A. Allam, Jamaan Ajarem, Zhongbo Wei, Zuoyao Wang. Impact of carbon nanotubes on the toxicity of inorganic arsenic [As(III) and As(V)] to Daphnia magna: the role of the certain arsenic species. Environmental Toxicology and Chemistry: Volume 35, Issue 7, pages 1852–1859, July 2016. DOI: 10.1002/etc.3340
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3340/full
     

Arsenic removal using natural biomaterial-based sorbents

Arsenic contamination of water is a major problem worldwide. A possible solution can be approached through developing new sorbents based on cost-effective and environmentally friendly natural biomaterials. We have developed new sorbents based on biomaterial impregnation with iron oxyhydroxide. In this study, raw peat material, iron-modified peat, iron-modified biomass (shingles, straw, sands, cane and moss) as well as iron humate were used for the removal of arsenate from contaminated water. The highest sorption capacity was observed in iron-modified peat, and kinetic studies indicated that the amount of arsenic sorbed on this material exceeds 90 % in 5 h. Arsenate sorption on iron-modified peat is characterised by the pseudo-second-order mechanism. The results of arsenic sorption in the presence of competing substances indicated that sulphate, nitrate, chloride and tartrate anions have practically no influence on As(V) sorption onto Fe-modified peat, whereas the presence of phosphate ions and humic acid significantly lowers the arsenic removal efficiency.     

Geochemical occurrences of arsenic and fluoride in bedrock groundwater: a case study in Geumsan County,Korea

Bedrock groundwaters in Geumsan County, Korea, were surveyed to investigate the distribution and geochemical behaviors of arsenic and fluoride, mobilized through geogenic processes. The concentrations were enriched up to 113 μg/L for arsenic and 7.54 mg/L for fluoride, and 16% of 150 samples exceeded World Health Organization drinking water guidelines for each element. Simple Ca-HCO₃ groundwater types and positive correlations with pH, Ca, SO₄, and HCO₃ were characteristics of high (>10 μg/L) As groundwaters. The oxidation reaction of sulfide minerals in metasedimentary rocks and locally mineralized zones seems to be ultimately responsible for the existence of arsenic in groundwater. Desorption process under high pH conditions may also control the arsenic mobility in the study area. High (>1.5 mg/L) F groundwaters were found in the Na-HCO₃ type and with greater depth. Fluoride seemed to be enriched by deep groundwater interaction with granitic rocks, and continuous supply to shallow Ca-HCO₃-type groundwater kept the concentration high. In the study area, drinking water management should include periodic As and F monitoring in groundwater.

     

Removal of arsenic from aqueous solution by two types of nano TiO2 crystals

Titanium dioxide (TiO₂) is a promising sorbent for As removal. There are two main and physico-chemically distinct polymorphs of TiO₂ in nature, namely anatase and rutile. Since the difference of arsenic removal by the two polymorphs of TiO₂ is now well known, study on the arsenic removal efficiency and the underlying mechanism is of great significance in developing new remediation strategies for As-polluted waters. Here batch experiments were carried out in combination with instrumental analysis of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) to investigate the effects, influential factors and mechanisms of As removal from aqueous solution by two types of nano TiO₂ crystals. The adsorption behavior of anatase and rutile for As(V) and As(III) are well described by Freundlich equations. Anatase had higher As removal efficiency and adsorption capacity than rutile. Solution pH had no influence on the As adsorption of anatase TiO₂, whereas the As removal by rutile TiO₂ was increased by 7?C18% with pH from 4 to 10. Presence of accompanying anions such as phosphate, silicate, nitrate and sulfate, decreased the As(V) and As(III) removal by both crystals, with phosphate being the most effective. However, removal of As by rutile TiO₂ was greatly enhanced in the presence of divalent cations i.e. Ca²⁺ and Mg²⁺. Shading of light decreased the removal of As(V) and As(III) of anatase by 15.5% and 17.5%, respectively, while a slight increase of As removal was observed in the case of Rutile TiO₂. FT-IR characterization of As(V) or As(III)-treated nano TiO₂ crystals indicated that both Ti-O and As-O groups participated in As adsorption. Both FT-IR and XPS analysis demonstrated that As(III) was photooxidated into As(V) when adsorbed by anatase under the light condition. Thus, the effect of crystal types and light condition on As removal should be taken into consideration when nano TiO₂ is applied for As removal from water.     

Metal immobilization by sludge-derived biochar: roles of mineral oxides and carbonized organic compartment

Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (Al₂O₃). Batch experiments were conducted at 25 and 45 °C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1–60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 °C than 25 °C for SDBC and AC, while the opposite was shown for Al₂O₃, indicating the significance of temperature-dependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on Al₂O₃ that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal–oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment.     

Removal of arsenate from water by adsorbents: a comparative case study

Laboratory and field filtration experiments were conducted to study the effectiveness of As(V) removal for five types of adsorbent media. The media included activated alumina (AA), modified activated alumina (MAA), granular ferric hydroxide (GFH), granular ferric oxide (GFO), and granular titanium dioxide (TiO₂). In laboratory batch and column experiments, the synthetic challenge water was used to evaluate the effectiveness for five adsorbents. The results of the batch experiments showed that the As(V) adsorption decreased as follows at pH 6.5: TiO₂ > GFO > GFH > MAA > AA. At pH 8.5, however, As(V) removal decreased in the following order: GFO = TiO₂ > GFH > MAA > AA. In column experiments, at pH 6.5, the adsorbed As(V) for adsorbents followed the order: TiO₂ > GFO > GFH, whereas at pH 8.5 the order became: GFO = TiO₂ > GFH when the challenge water containing 50 μg/L of As(V) was used. Field filtration experiments were carried out in parallel at a wellhead in New Jersey. Before the effluent arsenic concentration increased to 10 μg/L, approximately 58,000 and 41,500 bed volumes of groundwater containing an average of 47 μg/L of As(V) were treated by the filter system packed with GFO and TiO₂, respectively. The As(V) adsorption decreased in the following sequence: GFO > TiO₂ > GFH > MAA > AA. Filtration results demonstrated that GFO and TiO₂ adsorbents could be used as media in small community filtration systems for As(V) removal.     

Analytik von Umwandlungsprodukten des Schwefellosts (S-LOST)

The results of investigations of the aquatic ecotoxicity of sternutators and their metabolites (phenyl arsenic compounds) are presented. The standardized luminescence inhibition test (LumisTox, Dr. Lange) with the marine bacteriaVibrio fischeri was applied according to the German norm DIN 38412, part 34. All investigated organic AS(III) compounds exhibit EC₅₀-values (50 % inhibition of the luminescence) of less than 1 mg/l, whereas all investigated organic As(V) compounds and inorganic arsenic show EC₅₀-values exceeding 100 mg/l     

Validation of a digestion procedure for ICP-AES and dynamic reaction cell ICP-MS for trace elemental analysis in environmental samples

Due to chloride polyatomic interferences, hydrochloric acid is not recommended for preparation of samples analysed by ICP-MS and separate digestion procedures are used for ICP-MS and ICP-AES. Here we demonstrate that a single digestion procedure using a mixture of HNO₃ and HCl can be used for ICP-AES and dynamic reaction cell (DRC)-ICP-MS. Hotplate, block digester and microwave digestion were investigated. For a quantitative recovery of 26 elements including Ag, Sb and Ti from waters, soils and sediments, the final concentration of 10% (v/v) HCl in the digest is required regardless of the digestion techniques. The method detection limits of 0.3–1.2 μg/L were obtained for chloride-interfering elements As, V, Cr and Se by DRC-ICP-MS using ammonia and oxygen as the DRC gas.     

Chronic study of arsenic trioxide-induced hepatotoxicity in relation to arsenic liver accumulation in rats

This study measured activities of serum enzymes alkaline phosphatase, acid phosphatase, glutamic oxaloacetic transaminase (SGOT), and glutamic pyruvic transaminase (SGPT), markers of liver function in albino rats after continuous ingestion of arsenic trioxide (As₂0₃). For the study, treated animals were given AS₂O₃ (0.2 mg/100 g/day) orally for 180 days. After the completion of treatment, the blood was collected for the estimation of serum biochemical markers. The results obtained were compared with control group. Data showed a significant increase in SGOT and SGPT activity after 60 days of As₂0₃ administration. The level of alkaline phosphatase and acid phosphatase increased significantly after 90 and 120 days, respectively. Since the elevation of these serum enzymes is an indicator of hepatic damage, data indicate that As₂O₃ produces hepatotoxicity. When taken continuously, arsenic was also deposited in liver and blood and affected the enzymatic pathways. Total accumulated arsenic was determined by HG-AAS at 193.7 nm.     

Electro-assisted regeneration of ion exchange resins

Electro-assisted regeneration (EAR) for the mixed bed of strongly acidic cation and weakly basic anion exchange resins with the Al(OH)3 suspension in a three-compartment cell was investigated. The desalination experiments were carried out to evaluate the characteristic of the regenerated mixed resins. Experimental results showed that the efficiency of resin regeneration was strictly dependent on the voltage, regeneration time, and feed regenerant flow rate. The amount of the effluent reached 50 times the volume of the resins bed, and the conductivity was less than 1.0 μs/cm. Compared to the conventional ER, the total effluent volume of EAR was about 1000 mL more than that of ER under the same conditions, and the outlet conductivity was significantly lower. The desalination and regeneration reaction mechanisms of the mixed resins indicated the regeneration efficiency of resin with Al(OH)₃ as the regenerant was much higher than that with H₂O.     

As(V)-reduction to As(III) by arsenic-resistant Bacillus spp. bacterial strains isolated from low-contaminated sediments of the Oliveri-Tindari Lagoon,Italy

Five arsenic-resistant bacterial strains designated MT1, MT2, MT3, V1 and V2 were isolated from sediments of the Oliveri-Tindari Lagoon (Italy), which comprises six small lakes whose sediments contain low arsenic concentrations. Phylogenetic analysis of the 16S rRNA gene sequences assigned them to the genus Bacillus. Bacillus sp. strain MT3 showed higher tolerance to As(III) and As(V), as indicated by minimum inhibitory concentrations of 14 and 135 mmol^?1, respectively. Bacillus sp. strain V1 showed growth inhibition at 14 mmol^?1 in the presence of As(III) and at 68 mmol^?1 in the presence of As(V), whereas the arsenic resistance of Bacillus sp. strain MT1 was 10 and 27 mmol^?1 for As(III) and As(V), respectively. The strains Bacillus spp. MT2 and V2 showed low levels of As(III) and As(V) resistance, as it was unable to grow at concentrations>7 and 14 mmol^?1, respectively. The isolated arsenic-resistant Bacillus spp. strains were able to reduce As(V) to As(III), especially Bacillus spp. strain MT3. This study suggests that the isolated bacterial strains play a role in the arsenic biogeochemical cycle of arsenic-poor sediments in the Oliveri-Tindari Lagoon.     

Arsenic contamination: a potential hazard to the affected areas of West Bengal, India

Arsenic contamination in groundwater is becoming more and more a worldwide problem. Nearing 50 million of people are at health risk from arsenic contamination at Ganga–Meghna–Bramhaputra basin. The experimental results of the five blocks under Malda district of West Bengal, India, showed that the arsenic concentration in groundwater (0.41–1.01 mg/l) was higher than the permissible limit for drinking water (0.01 mg/l) (WHO) and FAO (Food and Agriculture Organization) permissible limit for irrigation water (0.10 mg/l). The soil arsenic level (13.12 mg/kg) crossed the global average (10.0 mg/kg), but within the maximum acceptable limit for agricultural soil (20.0 mg/kg) recommended by the European Union. The total arsenic concentration on food crops varied from 0.000 to 1.464 mg/kg of dry weight. The highest mean arsenic concentration was found in potato (0.456 mg/kg), followed by rice grain (0.429 mg/kg). The total mean arsenic content (milligrams per kg dry weight) in cereals ranged from 0.121 to 0.429 mg/kg, in pulses and oilseeds ranged from 0.076 to 0.168 mg/kg, in tuber crops ranged from 0.243 to 0.456 mg/kg, in spices ranged from 0.031 to 0.175 mg/kg, in fruits ranged from 0.021 to 0.145 mg/kg and in vegetables ranged from 0.032 to 0.411 mg/kg, respectively. Hence, arsenic accumulation in cereals, pulses, oilseed, vegetables, spices, cole crop and fruits crop might not be safe in future without any sustainable mitigation strategies to avert the potential arsenic toxicity on the human health in the contaminated areas.     

Quality of tube well water intended for irrigation and human consumption with special emphasis on arsenic contamination at the area of Punjab,Pakistan

In the present study, the tube well water quality and the associated health risks, emphasizing on arsenic contamination, were investigated in rural and urban samples from Tehsil Mailsi located in Punjab, Pakistan. Arsenic concentrations (μg/L) were ranged from 12 to 448.5 and which exceeded the WHO recommended limit (10 μg/L) in all cases. The calculated average daily dose (3.3 × 10^?0.4 to 1.2 × 10^?0.2 mg/kg day) and hazard quotient (1.1–40) reflected the potential health risk to local population due to tube well water consumption as drinking purpose. Sodium percent (Na%), sodium absorption ratio, residual sodium carbonate, Kelly’s index and magnesium absorption ratio were also determined to assess the suitability of tube well water for irrigation purpose. The resulting piper plot revealed the Na–Ca–HCO₃ type water chemistry of the area and generally alkaline environment. The spatial distribution of arsenic in the tube well waters pinpoints the significant contribution of anthropogenic activities to arsenic pollution. Nevertheless, different statistical tools, including principal component analysis, hierarchical cluster analysis and correlation matrices, revealed the contribution of both natural and anthropogenic activities and alkaline type of aquifers toward the high level of arsenic contamination.     

Total arsenic concentrations in Chinese children’s urine by different geographic locations,ages, and genders

Little is known about the variation of Chinese children’s exposure to arsenic by geography, age, gender, and other potential factors. The main objective of this study was to investigate the total arsenic concentration in Chinese children’s urine by geographic locations, ages, and genders. In total, 259 24-h urine samples were collected from 210 2- to 12-year-old children in China and analyzed for total arsenic and creatinine concentrations. The results showed that the upper limit (upper limit of the 90% confidence interval for the 97.5 fractile) was 27.51 µg/L or 55.88 µg/g creatinine for Chinese children. The total urinary arsenic levels were significantly different for children in Guangdong, Hubei, and Gansu provinces (P < 0.05), where the upper limits were 24.29, 58.70, and 44.29 µg/g creatinine, respectively. In addition, the total urinary arsenic levels were higher for 2- to 7-year-old children than for 7- to 12-year-old children (P < 0.05; the upper limits were 59.06 and 44.29 µg/g creatinine, respectively) and higher for rural children than for urban children (P < 0.05; the upper limits were 59.06 and 50.44 µg/g creatinine, respectively). The total urinary arsenic levels for boys were not significantly different from those for girls (P > 0.05), although the level for boys (the upper limit was 59.30 µg/g) was slightly higher than that for girls (the upper limit was 58.64 µg/g creatinine). Because the total urinary arsenic concentrations are significantly different for general populations of children in different locations and age groups, the reference level of total urinary arsenic might be dependent on the geographic site and the child’s age.     

Geological factors controlling occurrence and distribution of arsenic in groundwaters from the southern margin of the Duero Basin,Spain

Groundwater from springs and boreholes on the southern edge of the Cenozoic Duero Basin (DB) of Spain has concentrations of arsenic (As) which are commonly above the EC drinking-water limit of 10 μg/L and reach observed values up to 241 μg/L. Groundwater compositions within the sedimentary aquifer vary from Ca–HCO₃ type, variably affected by evaporation and agricultural pollution at shallow levels, to Na–HCO₃ compositions in deeper boreholes of the basin. Groundwater conditions are mainly oxidising, but reducing groundwaters exist in sub-basins within the aquifer, localised flow paths likely being influenced by basement structure. Arsenic concentrations are spatially variable, reaching up to 38 μg/L in springs of the Spanish Central System (SCS) basement aquifer and up to 62 μg/L in springs from the DB. Highest As concentrations are associated with the Na–HCO₃ compositions in deep boreholes (200–450 m depth) within the DB. These have high pH values (up to 9.6) which can give rise to associated elevated concentrations of V and U (up to 64 and 30 μg/L, respectively). In the deep borehole waters of the DB, oxidising flows derived from the mineralised igneous–metamorphic basement and discharging via major faults, and are considered the origin of the higher concentrations. Compositions are consistent with desorption of As and other anionic species from metal oxyhydroxides in an oxic environment. Under locally reducing conditions prevalent in some low-flow parts of the DB, an absence of detectable dissolved As is coincident with low or undetectable SO₄ concentrations, and consistent with loss via formation of authigenic sulphide minerals. Mitigation measures are needed urgently in this semi-arid region where provision of alternative sources of safe drinking water is logistically difficult and expensive.     

Efficient uranium immobilization on red clay with phosphates

Uranium is a very toxic and radioactive element. Removal of uranium from wastewaters requires remediation technologies. Actual methods are costly and ineffective when uranium concentration is very low. Little is known about the enhancement of sorption of uranyl ions by phosphate ions on aluminosilicates. Here, we studied sorption of uranyl acetate on red clay in the presence of phosphates. The concentration of U(VI) ranged 0.0001–0.001 mol/L, whereas the concentration of PO₄ ^3? was constant at 0.0001 mol/L. We designed a new method for the analysis of ternary surface complexes. We observed for the first time a remarkable improvement of U(VI) sorption on red clay under the influence of phosphates. We also found that at least two different ternary surface complexes U(VI)–phosphate–clay are formed in the sorbent phase. The complexation of UO₂ ²⁺ cations by phosphate ligands in the sorbent phase was confirmed by the X-ray photoelectron spectra of U 4f electrons.