Mechanism analysis of the immobilization of heavy metal ions with the water-soluble polymer: The influence of resin structure and the further adsorption of chelate.

Polymer materials have become one of the potential materials for remediation of heavy metal (HM) contamination in water and soil. However, the specific advantages of polymers are rarely studied. Water-soluble thiourea formaldehyde resin (WTF) is one of the effective polymer amendments. Through leaching experiments, WTF can stabilize 93.0% of Cd2+ and 99.7% of Cu2+. The results of HM morphology analysis show that after adding WTF, most of the HMs have been transformed into a relatively stable state. For example, in the process of remediation of 6 mg/kg Cd contaminated soil, the proportion of acid-soluble Cd decreased from 56.5% to 12.8%, and the residual state increased from 13.5% to 45.4%. Compared with the resin-free structure, the three-dimensional structure of the resin plays an important role, but the efficiency of precipitation with HMs is doubled. According to the simulation of the adsorption process by Materials Studio, the characterization of the scanning electron microscope-energy dispersive instrument and the results of the adsorption experiment, in the solution, the precipitate formed by WTF and Cd2+ has multilayer adsorption of HMs, and can further adsorb HM by -OH. Soil enzyme activity experiments proved that the risk of secondary pollution by adding WTF is rare, and even WTF can achieve the effect of slow-release nitrogen fertilizer. In the WTF remediation process, the biological toxicity reduction of HMs is result from, on the one hand, the complexation of functional group of WTF; on the other hand, the resin structure of WTF; in addition, multi-layer adsorption and adsorption of end groups in the precipitation formed by WTF and HM. This work provides a theoretical basis for the potential capabilities of water-soluble resins and is beneficial to the design and development of subsequent amendments.

Effect of water-soluble thiourea formaldehyde (WTF) on soil contaminated with high copper (â ¡) concentration.

It is very important to seek a heavy metal soil stabilization/solidification (S/S) agent that has less risk of secondary release and has less impact on the soil. This study explored the repair effect of a new resin repair agent water-soluble thiourea-formaldehyde (WTF), and its stability under indigenous biodegradation and compared the repair effect with sodium sulfide (Na2S) and hydroxyapatite (HAP). Diethylene triamine pentaacetic acid leaching experiments show that WTF can effectively solidify/stabilize 97.9-84.7% of Cu. At the same time, heavy metal speciation analysis experiments show that WTF does indeed convert the exchangeable Cu in the soil into a non-exchangeable form. Research on soil organic matter, biological carbon and enzyme activity after remediation shows that WTF has a more positive effect on soil function, compared with HAP and Na2S. Experiments using indigenous microorganisms to decompose the precipitation formed by WTF and Cu show that under the condition of less impact on soil microorganisms, the risk of secondary release of heavy metals caused by soil microorganisms after WTF remediation is less. These findings provide valuable experience for understanding the role of resin structure in preventing the secondary release of heavy metals and restoring soil function.

Assessment of water-soluble thiourea-formaldehyde (WTF) resin for stabilization/solidification (S/S) of heavy metal contaminated soils.

Stabilization/Solidification (S/S) can be regarded as necessary for remediation of heavy metal contaminated soil. There is, however, solid agent is not very convenient to use. Water-soluble thiourea-formaldehyde (WTF) is a novel chelating agent, which has more practical applications. The process of WTF resin for S/S process of heavy metal contaminated soils was studied. Laboratory-prepared slurries, made of field soils spiked with Cd2+ and Cr6+ were treated with WTF resin. The toxicity characteristic leaching procedure (TCLP) showed that with 2 wt% WTF, in the neutral condition of soil after treatment for 7 d, the leaching concentrations of Cd2+ and Cr6+ in contaminated soil were decreased by 80.3% and 92.6% respectively. Moreover, Tessier sequence extraction procedure showed WTF resin reduced the leaching concentration by transforming heavy metal from exchange form to organic form. The structure of WTF is obtained according to elemental analysis result and reaction mechanism. Through analysis of the infrared spectrogram of WTF and WTF heavy mental chelating precipitation, WTF can form stable chelate with heavy mental through coordination. The significant groups are hydroxyl, nitrogen and sulphur function groups in WTF mainly. Toxicology test revealed that the WTF resin is nontoxic to microorganism in the soils.

Synthesis of a water-soluble thiourea-formaldehyde (WTF) resin and its application to immobilize the heavy metal in MSWI fly ash.

Because of the high concentrations of heavy metals, municipal solid waste incineration (MSWI) fly ash is classified as a hazardous waste, which need to be treated to avoid damaging the environment. A novel water-soluble thiourea-formaldehyde (WTF) resin was synthesized by two step reactions (hydroxymethylation reaction and condensation reaction) in the laboratory. Synthetic conditions, removal of free formaldehyde in the resin and the ability of immobilization heavy metals in the MSWI fly ash were studied. The possible molecular structure of the resin was also discussed by elemental analysis and FTIR spectra. Experimental results showed that the synthesis conditions of WTF resin were the formaldehyde/thiourea (T/F) mole ratio of 2.5:1, hydroxymethylation at pH 7.0-8.0 and 60 °C for 30min, and condensation of at pH 4.5-5.0 and 80 °C. In addition, the end point of condensation reaction was measured by turbidity point method. The result of elemental analysis and FTIR spectra indicated that thiourea functional group in the WTF resin chelated the heavy metal ions. Melamine can efficiently reduce the free formaldehyde content in the resin from 8.5% to 2%. The leaching test showed that the immobilization rates of Cr, Pb and Cd were 96.5%, 92.0% and 85.8%, respectively. Leaching concentrations of Cr, Pb and Cd in the treated fly ash were decreased to 0.08 mg/L, 2.44 mg/L and 0.23 mg/L, respectively. The MSWI fly ash treated by WTF resin has no harm to the environment.

An anaerobic two-layer permeable reactive biobarrier for the remediation of nitrate-contaminated groundwater.

In this paper, an anaerobic two-layer permeable reactive biobarrier system consisting of an oxygen-capturing layer followed by a biodegradation layer was designed firstly for evaluating the remediation effectiveness of nitrate-contaminated groundwater. The first layer filling with granular oxygen-capturing materials is used to capture dissolved oxygen (DO) in groundwater in order to create an anaerobic condition for the microbial denitrification. Furthermore, it can also provide nutrition, such as carbon and phosphorus, for the normal metabolism of immobilized denitrifying bacteria filled in the second layer. The second layer using granular activated carbon as microbial carrier is able to biodegrade nitrate entering the barrier system. Batch experiments were conducted to identify the effect of DO on microbial denitrification, oxygen-capturing performance of zero valent iron (ZVI) powder and the characteristics of the prepared oxygen-capturing materials used to stimulate growth of denitrifying bacteria. A laboratory-scale experiment using two continuous upflow stainless-steel columns was then performed to evaluate the feasibility of this designed system. The first column was filled with granular oxygen-capturing materials prepared by ZVI powder, sodium citrate as well as other inorganic salts, etc. The second column was filled with activated carbon immobilizing denitrifying microbial consortium. Simulated nitrate-contaminated groundwater (40 mg NO3-N/L, pH 7.0) with 6 mg/L of DO content was pumped into this system at a flow rate of 235 mL/d. Samples from the second column were analyzed for nitrate and its major degradation byproduct. Results showed that nitrate could be removed more than 94%, and its metabolic intermediate, nitrite, could also be biodegraded further in this passive system. Further study is necessary in order to evaluate performance of its field application.

Laboratory column study for remediation of MTBE-contaminated groundwater using a biological two-layer permeable barrier.

In this study, an in situ biological two-layer permeable reactive barrier system consisting of an oxygen-releasing material layer followed by a biodegradation layer was designed to evaluate the remediation effectiveness of MTBE-contaminated groundwater. The first layer containing calcium peroxide (CaO(2)) and other inorganic salts is to provide oxygen and nutrients for the immobilized microbes in the second layer in order to keep them in aerobic condition and maintain their normal metabolism. Furthermore, inorganic salts such as potassium dihydrogen phosphate (KH(2)PO(4)) and ammonium sulphate ((NH(4))(2)SO(4)) can also decrease the high pH caused by the alkali salt degraded from CaO(2). The second layer using granular expanded perlite as microbial carrier is able to biodegrade MTBE entering the barrier system. Batch experiments were conducted to identify the appropriate components of oxygen-releasing materials and the optimum pH value for the biodegradation of MTBE. At pH=8.0, the biodegradation efficiency of MTBE is the maximum and approximately 48.9%. A laboratory-scale experiment using two continuous upflow stainless-steel columns was then performed to evaluate the feasibility of this designed system. The fist column was filled with oxygen-releasing materials at certain ratio by weight. The second column was filled with expanded perlite granules immobilizing MTBE-degrading microbial consortium. Simulated MTBE-contaminated groundwater, in which dissolved oxygen (DO) content was 0mg/L, was pumped into this system at a flow rate of 500mL/d. Samples from the second column were analyzed for MTBE and its major degradation byproduct. Results showed that MTBE could be removed, and its metabolic intermediate, tert-butyl alcohol (TBA), could also be further degraded in this passive system.