Adsorptive Performances of Alkaline Treated Peat for Heavy Metal Removal

Efficient Lead Pb(II) Removal with Chemically Modified Nostoc commune Biomass

A new biosorbent based on Nostoc commune (NC) cyanobacteria, chemically modified with NaOH (NCM), has been prepared, characterized and tested as an effective biomass to remove Pb(II) in aqueous media. The adsorption capacity of NCM was determined to be qe = 384.6 mg g−1. It is higher than several other biosorbents reported in the literature. Structural and morphological characterization were performed by FTIR, SEM/EDX and point zero of charge pH (pHPZC) measurements. NCM biosorbent showed more porous surfaces than those NC with heterogeneous plates including functional adsorption groups such as OH, C = O, COO−, COH or NH. Optimal Pb(II) adsorption occurred at pH 4.5 and 5.5 with a biomass dose of 0.5 g L−1. The experimental data of the adsorption process were well fitted with the Freundlich-isotherm model and pseudo-2nd order kinetics, which indicated that Pb(II) adsorption was a chemisorption process on heterogeneous surfaces of NCM. According to the thermodynamic parameters, this process was exothermic (∆H0 < 0), feasible and spontaneous (∆G0 < 0). NCM can be regenerated and efficiently reused up to 4 times (%D > 92%). NCM was also tested to remove Pb (%R~98%) and Ca (%R~64%) from real wastewater.

Modification of Natural Peat for Removal of Copper Ions from Aqueous Solutions

This study aimed at estimating peat adsorption properties for copper ion removal from aqueous solutions during peat modification. Two peat modifications have been studied using batch tests and quantitatively reproduced with instrumental analysis by using spectrometric, potentiometric, and thermodynamic modeling methods. The first variation—mechanical activation—was carried out in a planetary mill; for the second one—mechanochemical activation—dry sodium percarbonate (Na2CO3∙1.5H2O2) was added. The adsorption of copper ions was studied in the concentration range from 10–150 mg/L with an interaction time from 0.25–12 h. Both modifications led to significant changes in the interaction energy in the adsorption layer; thus, the acceptor properties of macromolecules were enhanced from natural peat to mechanically activated peat and mechanochemically activated peat. FTIR spectra, specific surface area characteristics, and sorption experiments show the predominantly chemical nature of copper sorption. Maximum adsorption capacity was determined to be 24.1, 42.1, and 16.0 mg/g for natural peat, mechanically activated peat, and mechanochemically activated peat, respectively. The example of peat mechanochemically oxidized with Na2CO3∙1.5H2O2 shows that the improvement in the physicochemical properties (CBET and specific surface area) plays a smaller role in the sorption capacity in relation to copper ions than the presence of phenolic and carboxyl groups, the content of which decreases during oxidation.

Suitability of natural and chemically modified peat as a sorbent material for mining water purification in small-scale pilot systems

In this study, the suitability of natural peat (Nat-Peat) and HCl-modified peat (M-Peat) as a sorbent for purification of mining water was evaluated in two different small-scale pilot systems: a continuous stirred tank reactor (CSTR) and a horizontal flow filter (HFF). The effect of process parameters (peat type, peat dose, mixing time, mixing intensity) on metal (metalloid) removal in the CSTR system was also investigated. In the CSRT, Nat-Peat achieved higher removal of Ni (<80%) and As (∼61%) than M-Peat (72% and 26% for Ni and As, respectively). In the HFF, Nat-Peat achieved slightly lower maximum removal of Ni (<96%) than M-Peat (<98%) and higher removal of As and Sb (<87% and 8%) than M-Peat (<35% and 7%). Thus, chemical modification (HCl) of peat did not improve its affinity for metal and metalloids. Among the process parameters studied, peat dose exerted the strongest effect on residual concentrations of Ni, As and Sb. Higher removal of Ni and As was achieved in treatment combinations involving high peat dose (2 g/L), mixing time (60 min) and mixing intensity (300 rpm), but the effect of increasing level of these factors was not linear. This study showed that peat can be a viable sorbent material in CSTR systems (followed by sedimentation) if sorbent particle removal can be improved. Use of peat in HFF systems is not viable, due to its inability to cope with large water volumes.

Removal of metals from wastewaters by mineral and biomass-based sorbents applied in continuous-flow continuous stirred tank reactors followed by sedimentation

Numerous studies have examined the performance of mineral and biomass-based sorbents for metal removal under laboratory conditions, but few pilot-scale tests have been performed on possible water purification systems in which these sorbents can be used. This study addressed this issue by evaluating the suitability of selected sorbents for use in continuous-flow continuous stirred tank reactors (CSTR) followed by sedimentation in laboratory and in situ pilot-scale experiments. Acid (HCl)-modified peat (M-Peat), a commercially available mineral sorbent containing mainly magnesium (Mg) carbonates, Mg oxides and Mg silicates (Mineral-P) and a calcium-rich ground granular blast furnace slag (by-product of stainless steel production (Slag) were tested for treatment of metallurgical industry wastewater (laboratory, pilot). Overall, higher metal removal was achieved from samples with higher initial metal concentrations. M-Peat achieved good removal of Zn (50-70%) and Ni (30-50%) in laboratory and pilot experiments. However, the poor settling characteristics of M-Peat can restrict its application in systems where sedimentation is the solid-liquid separation process applied. Mineral-P showed good performance in removing 65-85% of Zn present in the water and it performed similarly in laboratory and pilot tests. However, low concentrations of As and Ni leached from Mineral-P in all tests. Slag achieved good performance in treatment of the industrial wastewater, removing 65-80% of Zn and 60-80% of Pb during pilot tests. However, low concentrations of Cr and Cu were leached from Slag in a few tests. As a by-product of the same (metallurgical) industry, ground granular blast furnace slag is an excellent candidate for reducing Zn concentrations from industrial wastewater flows.

Single-Step Synthesis of Magnesium-Doped Lithium Manganese Oxide Nanosorbent and Their Polymer Composite Beads for Selective Heavy Metal Removal

Magnesium-doped lithium manganese oxide nanosorbent is prepared by a single-step solid-state method and characterized with appropriate analytical techniques, adsorption kinetic model, and isotherms. Competitive and noncompetitive adsorption studies are performed for a range of heavy metal ions. Prepared nanosorbent has shown explicit selectivity for various heavy metal ions and no remarkable influence of coexisting common interfering ions (Na⁺, K⁺, Mg²⁺, and Ca²⁺), which generally coexist with all natural sources of water, contaminated water, and industrial waste. To achieve easy handling of an adsorbent, polysulfone-nanosorbent (PS-nanosorbent) composite beads are prepared, and their competitive heavy metal removal performance is determined. Competitive adsorption and regeneration studies have shown that PS-nanosorbent beads can be employed for selective heavy metal removal and reuse for multiple cycles.

Steam activation of waste biomass: highly microporous carbon, optimization of bisphenol A, and diuron adsorption by response surface methodology

Highly microporous carbons were prepared from argan nut shell (ANS) using steam activation method. The carbons prepared (ANS@H2O-30, ANS@H2O-90, and ANS@H2O-120) were characterized using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared, nitrogen adsorption, total X-ray fluorescence, and temperature-programmed desorption (TPD). The ANS@H2O-120 was found to have a high surface area of 2853 m2/g. The adsorption of bisphenol A and diuron on ANS@H2O-120 was investigated. The isotherm data were fitted using Langmuir and Freundlich models. Langmuir isotherm model presented the best fit to the experimental data suggesting micropore filling of ANS@H2O-120. The ANS@H2O-120 adsorbent demonstrated high monolayer adsorption capacity of 1408 and 1087 mg/g for bisphenol A and diuron, respectively. The efficiency of the adsorption was linked to the porous structure and to the availability of the surface adsorption sites on ANS@H2O-120. Response surface method was used to optimize the removal efficiency of bisphenol A and diuron on ANS@H2O-120 from aqueous solution. Graphical abstract ᅟ.

Valorisation possibilities of exhausted biosorbents loaded with metal ions - A review

Biosorption is considered one of the most promising methods for removal of metal ions from aqueous effluents, due to its low-cost and eco-friendly characteristics. However, the exhausted biosorbents loaded with metal ions, obtained at the end of biosorption processes, are still a problem which should be solved to increase the applicability of biosorption on an industrial scale. In this study are examined three possibilities for the valorisation of exhausted biosorbents loaded with metal ions, namely: (i) regeneration and reuse of biosorbents in multiple biosorption cycles, (ii) the use of exhausted biosorbents as fertilizers for soils poor in essential microelements, and (iii) the pyrolysis of exhausted biosorbents, under well defined conditions. The main advantages and disadvantages of each valorisation possibility are reviewed in order to find the best way to use these cheap materials in accordance with the principles of the circular economy and thereby contributing to the development of sustainable biosorption technology.

Iron-loaded Sphagnum moss extract residue for phosphate removal

Sphagnum moss extract residue (SMER), obtained after pressurized hot water extraction, was modified with Fe(III) and investigated for phosphate sorption. Although moss extract contains value-added compounds, SMER is considered to be waste until suitable uses can be developed. The effect of modification conditions were investigated, i.e. different initial Fe(III) concentrations (0.024, 0.048 and 0.072 mol/L Fe³⁺) and modification pH values (5, 7 and 9). A modification pH of 5 and the highest initial Fe(III) concentration (0.072 mol/L Fe³⁺) resulted in the highest phosphate removal efficiency, and thus was selected for further study. The removal efficiency was found to decrease with increasing pH in the range of 3-9. Maximum removal efficiency (82%) for phosphate sorption was observed at pH 3 after 24 h contact time (dosage 2 g/L, initial concentration 15 mg P/L). With increased contact time, the phosphate removal efficiency improved and reached equilibrium within 48 h. The Elovich model was found to provide the best fit to the kinetic data. A capacity of 9-13 mg P/g was obtained with a 24-h contact time at pH 4. A good fit was achieved with the Redlich-Peterson equation. FTIR analysis confirmed that carboxylic acid groups were involved in the modification process. X-ray diffraction analyses showed that amorphous two-line ferrihydrite was precipitated onto SMER, which was supported by X-ray photoelectron spectroscopy analyses.

Removal of metals from industrial wastewater and urban runoff by mineral and bio-based sorbents

The study was performed to evaluate chemically modified biosorbents, hydrochloric acid treated peat (HCl-P) and citric acid treated sawdust (Citric acid-SD) for their metal removal capacity from dilute industrial wastewater and urban runoff and compare their efficiency with that of commercially available mineral sorbents (AQM PalPower M10 and AQM PalPower T5M5 magnetite). Batch and column experiments were conducted using real water samples to assess the sorbents' metal sorption capacity. AQM PalPower M10 (consisting mainly of magnesium, iron and silicon oxides) exhibited excellent Zn removal from both industrial wastewater and spiked runoff water samples even at low dosages (0.1 g/L and 0.05 g/L, respectively). The high degree of Zn removal was associated with the release of hydroxyl ions from the sorbent and subsequent precipitation of zinc hydroxide. The biosorbents removed Ni and Cr better than AQM PalPower M10 from industrial wastewater and performed well in removing Cr and Cu from spiked runoff water, although at higher dosages (0.3-0.75 g/L). The main mechanism of sorption by biosorbents was ion exchange. The sorbents required a short contact time to reach equilibrium (15-30 min) in both tested water samples. AQM PalPower T5M5 magnetite was the worst performing sorbent, leaching Zn into both industrial and runoff water and Ni into runoff water. Column tests revealed that both HCl-P and AQM PalPower M10 were able to remove metals, although some leaching was witnessed, especially As from AQM PalPower M10. The low hydraulic conductivity observed for HCl-P may restrict the possibilities of using such small particle size peat material in a filter-type passive system.

Enhancing peat metal sorption and settling characteristics

Peat is an excellent material for metal sorption since it naturally contains different kinds of functional groups that can sorb metal cations from water. The main objective of this work was to test low-cost treatment (acid and alkali) methods for natural peat, which would improve the settling properties of peat particles while maintaining its metal removal efficiency. Particularly, the poor settling properties of peat hinder its practical application. The study revealed that NaOH-treated peat (0.1M) had excellent settling properties and could be applied in wastewater applications having mixing and settling systems without a settling aid. The superior leaching of humic and fulvic acids in alkaline treatment caused a change in morphology, making it a harder and sticky material. Moreover, the NaOH-treated (0.1M) peat was proven to be the most efficient material for nickel removal followed by the HCl-treated (0.2M) peat, citric acid-treated (0.16M) peat and water-treated peat. A higher temperature and longer time slightly increased the Ni removal efficiency with NaOH-treated peat material. The settling of HCl-treated peat was studied further using polyacrylamide flocculants (cationic, neutral, anionic). Cationic flocculants performed best and the cationic charge density also had an effect on the flocculation performance of peat particles. This study provides further evidence that peat can be applied in the treatment of metal-containing wastewaters.

Sorption potential of alkaline treated straw and a soil for sulfonylurea herbicide removal from aqueous solutions: An environmental management strategy

The adsorption potential of alkaline treated straw (wheat and corn) in mixture with soil, has been investigated for the removal of sulfonylurea molecules from an aqueous solutions. The surface characteristics were investigated by scanning electron microscopy and Fourier Transform Infrared - FTIR, while the adsorbent capacity was evaluated using batch sorption tests and liquid chromatography coupled with mass spectrometry. Surface analysis of alkaline treated straw samples by scanning electron microscopy - SEM showed the increasing of the surface roughness improving their functional surface activity. An increase (337.22 mg g^-1) of adsorption capacity of sulfonylurea molecules was obtained for all studied straw. The Langmuir isotherm model was the best model for the mathematical description of the adsorption process indicating the forming of a surface sorption monolayer with a finite number of identical sites. The kinetics of sulfonylurea herbicide followed the pseudo-second order mechanism corresponding to strong chemical interactions. The results sustained that the alkaline treated straw have biosorption characteristics, being suitable adsorbent materials.

Optimization of process parameters for heavy metals biosorption onto mustard waste biomass

Mustard waste biomass was tested as a biosorbent for the removal of Pb(II), Zn(II) and Cd(II) from aqueous solution. This strategy may be a sustainable option for the utilization of such wastes. The influence of the most important operating parameters of the biosorption process was analyzed in batch experiments, and optimal conditions were found to include initial solution pH 5.5, 5.0 g biosorbent/L, 2 hours of contact time and high temperature. Kinetics analyses show that the maximum of biosorption was quickly reached and could be described by a pseudo-second order kinetic model. The equilibrium data were well fitted by the Langmuir model, and the highest values of maximum biosorption capacity were obtained with Pb(II), followed by Zn(II) and Cd(II). The thermodynamic parameters of the biosorption process (ΔG, ΔH and ΔS) were also evaluated from isotherms. The results of this study suggest that mustard waste biomass can be used for the removal of heavy metals from aqueous media.