The use of low-cost adsorbents for wastewater purification in mining industries

Enhanced reduction of sulfate by iron-carbon microelectrolysis: interaction mechanism between microelectrolysis and microorganisms

Sulfate wastewater has a wide range of sources and greatly harms water, soil, and plants. Iron-carbon microelectrolysis (IC-ME) is a potentially sustainable strategy to improve the treatment of sulfate (SO42-) wastewater by sulfate-reducing bacteria (SRB). In this study, an iron-carbon mixed micro-electrolysis bioreactor (R1), iron-carbon layered bioreactor (R2), activated carbon bioreactor (R3), and scrap iron filing bioreactor (R4) were constructed by up-flow column experimental device. The performance and mechanism of removing high-concentration sulfate wastewater under different sulfate concentrations, hydraulic retention times (HRT), and chemical oxygen demand (COD)/SO42- were discussed. The results show that the iron-carbon microelectrolysis-enhanced SRB technology can remove high-concentration sulfate wastewater, and the system can still operate normally at low pH. In the high hydraulic loading stage (HRT = 12 h, COD/SO42-  = 1.4), the SO42- removal rate of the R1 reactor reached 98.08%, and the ORP value was stable between - 350 and - 450 mV, providing a good ORP environment for SRB. When HRT = 12 h and influent COD/SO42-  = 1.4, the R1 reactor sulfate removal rate reached 96.7%. When the influent COD/SO42-  = 0.7, the sulfate removal rate was 52.9%, higher than the control group. Biological community analysis showed that the abundance of SRB in the R1 reactor was higher than that in the other three groups, indicating that the IC-ME bioreactor could promote the enrichment of SRB and improve its population competitive advantage. It can be seen that the synergistic effect between IC-ME and biology plays a vital role in the treatment of high-concentration sulfate wastewater and improves the biodegradability of sulfate. It is a promising process for treating high-concentration sulfate wastewater.

Recent Advanced Development of Acid-Resistant Thin-Film Composite Nanofiltration Membrane Preparation and Separation Performance in Acidic Environments

Membrane filtration technology has attracted extensive attention in academia and industry due to its advantages of eco-friendliness related to environmental protection and high efficiency. Polyamide thin-film composite nanofiltration (PA TFC NF) membranes have been widely used due to their high separation performance. Non-acid-resistant PA TFC NF membranes face tremendous challenges in an acidic environment. Novel and relatively acid-resistant polysulfonamide-based and triazine-based TFC NF membranes have been developed, but these have a serious trade-off in terms of permeability and selectivity. Hence, how to improve acid resistance of TFC NF membranes and their separation performance in acidic environments is a pivotal issue for the design and preparation of these membranes. This review first highlights current strategies for improving the acid resistance of PA TFC NF membranes by regulating the composition and structure of the separation layer of the membrane performed by manipulating and optimizing the construction method and then summarizes the separation performances of these acid-resistant TFC NF membranes in acidic environments, as studied in recent years.

Adsorption Kinetics and Isotherms of Cu(II) and Fe(II) Ions from Aqueous Solutions by Fly Ash-Based Geopolymer

This paper describes the adsorption of Cu2+ and Fe2+ ions, common heavy metals found in industrial wastewater, by a fly ash-based geopolymer in batch adsorption experiments. Kinetics studies showed that the adsorption of each ion followed a pseudo-second order reaction. Moreover, adsorption isotherm of Cu2+ and Fe2+ ions followed the Langmuir model. Monolayer adsorption capacities were approximately 53.76 mg/g for Cu2+ ion and 52.63 mg/g for Fe2+ ion, respectively.

Facile fabrication and characterization of kenaf core as natural biochar for the highly efficient removal of selected endocrine-disrupting compounds

This study aims to formulate and fabricate the optimum condition of modified kenaf core (MKC) for the removal of targeted endocrine-disrupting compounds in a batch adsorption system. Kenaf core was chemically modified using phosphoric acid as an activating agent, which involved the pyrolysis step. Results indicated a significant difference (p < 0.05) for unmodified and novel modified biochar, observed in characteristic performance analysis via ultimate analysis, Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR) spectrum, and Brunauer-Emmett-teller (BET) surface area. The removal percentage of 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) in individual and binary mixture systems was examined in order to ascertain the highest removal percentage for MKC application in an aqueous solution. The main and interaction effects of three prepared variables such as incorporate of impregnation concentration of an acid catalyst (0.1-1.0 M), particle size (45-1,000 µm), and dosage (1.0-20.0 g/L) were examined and statistically analyzed via design of experiment (DoE) through developed quadratic models. The removal efficiency of E2 and EE2 in an individual system leads to T₂KC > T₁KC > T₃KC, whereas that in the binary mixture system leads to T₂KC > T₁KC > T₃KC and T₁KC > T₂KC > T₃KC for E2 and EE2 adsorption, respectively, through hydrogen bonding and the π-π interaction mechanism. Thus, the findings revealed T₂KC at a moderate level of acid concentration (0.5 M H₃PO₄) to be a potential biochar, with an environmentally safe and sound profile for opposing emerging pollutant issues as well as for the attainment of sustainable development goals.

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.

Evaluating the treatment of heavy metals in acidic wastewater by activated carbon

The study investigated the use of activated carbon (AC), produced from pinewood, to remove copper, zinc and iron from modified landfill leachates. South Africa faces an imminent water crisis, hence the need to see wastewater as an important source that must be treated and reused to combat water deficits in future. The use of AC as a soil amendment for the removal of heavy metals (HM) is not well researched. This study aimed to determine the ideal amount of AC (5%, 10%, 15% and 20% [w/w]) to add to soil using leaching columns for optimum HM adsorption. Modified acidic wastewater (pH > 2) was leached through soil columns packed with sandy loam soil and different amounts of AC (5%, 10%, 15% and 20% [w/w]). The results indicated that all the columns efficiently removed 94% copper, 80% zinc and 99% iron. Even a small amount (5% w/w) of AC was effective in removing HMs and can thus be considered as a possible cost-effective treatment option for acidic wastewater.

Microbiological Sulfide Removal-From Microorganism Isolation to Treatment of Industrial Effluent

Management of excessive aqueous sulfide is one of the most significant challenges of treating effluent after biological sulfate reduction for metal recovery from hydrometallurgical leachate. The main objective of this study was to characterize and verify the effectiveness of a sulfide-oxidizing bacterial (SOB) consortium isolated from post-mining wastes for sulfide removal from industrial leachate through elemental sulfur production. The isolated SOB has a complete sulfur-oxidizing metabolic system encoded by sox genes and is dominated by the Arcobacter genus. XRD analysis confirmed the presence of elemental sulfur in the collected sediment during cultivation of the SOB in synthetic medium under controlled physicochemical conditions. The growth yield after three days of cultivation reached ~2.34 g_protein/mol_sulfid, while approximately 84% of sulfide was transformed into elemental sulfur after 5 days of incubation. Verification of isolated SOB on the industrial effluent confirmed that it can be used for effective sulfide concentration reduction (~100% reduced from the initial 75.3 mg/L), but for complete leachate treatment (acceptable for discharged limits), bioaugmentation with other bacteria is required to ensure adequate reduction of chemical oxygen demand (COD).

Characterization of Fe-based sediments received from chemical pre-treatment of hydrometallurgical waste leachate from the recycling of alkaline batteries

The waste leachate from the hydrometallurgical recycling of spent batteries contains a significant amount of undesirable iron that needs to be precipitated before the recovery of target metals. The produced Fe-sediments are usually disposed of or stored at the treatment site as waste and are often poorly managed. This work estimates the environmental stability and application potential of Fe-sediments produced from highly acidic hydrometallurgical leachate during the recycling of spent alkaline batteries. After pH neutralization of the leachate by Na₂CO₃, a primary Fe-sediment (PFS), mainly composed of highly unstable metal (i.e., Fe, Zn, and Mn) sulfates, was obtained. The subsequent rinsing of this unstable PFS sediment led to the production of a secondary Fe-sediment (SFS), which was composed of an amorphous-phased ferric iron sulfate hydrate - Fe₁₆O₁₆(SO₄)₃(OH)₁₀·10H₂O. The results of single extraction using chemical reagents and biological dissolution by iron-transforming bacteria confirmed that despite most of the ions in PFS were dissolvable, the processed SFS was environmentally safe. The sorption efficiency of SFS towards Pb(II) and As(V) (up to ~ 99% and 94%, respectively, with an initial concentration of 100 mg/L) was found to be promising, suggesting the high potential for economical reuse of SFS.

Ecotoxicity assessment of a molybdenum mining effluent using acute lethal, oxidative stress, and osmoregulatory endpoints in zebrafish (Danio rerio)

The present study investigated the ecotoxicity of raw mining effluent from the largest molybdenum (Mo) open-pit mine in the Qinling mountains, China, and the treated effluent with neutralization and coagulation/adsorption processes, using zebrafish (Danio rerio). The results showed the following: (1) the mining effluent is acid mine drainage (AMD) and is highly toxic to zebrafish with a 96-h median lethal concentration (LC₅₀) of 3.80% (volume percentage) of the raw effluent; (2) sublethal concentrations of the raw effluent (1/50, 1/10, and 1/2 96-h LC₅₀) induced oxidative stress and osmoregulatory impairment, as reflected by the alterations in activities of superoxide dismutase and catalase and contents of malondialdehyde, and inhibition of Na⁺, K⁺-ATPase activity in gills and muscle after 28 days of sub-chronic exposure when compared with the unexposed group; and (3) the treatment of the raw effluent with neutralizer (NaOH) and adsorbent activated carbon reduced the acute lethal effect of raw effluent. The used endpoints including acute lethal and biochemical parameters related to oxidative stress and osmoregulatory impairment in zebrafish are cost-effective for toxicity assessment of AMD like the studied Mo mining effluent. Mining effluent management strategies extended by these results, i.e., the restriction of discharging raw and diluted effluent to adjacent waterways and the introduction of bio-monitoring system across all mining drainages in this area, were also proposed and discussed.

Removal of nickel from aqueous solution using synthesized IL/ZnO NPs

In this paper, the removal of nickel from aqueous solution was studied using zinc oxide nanoparticles (ZnO NPs) and zinc oxide nanoparticles functionalized ionic liquid (IL/ZnO NPs) by batch adsorption and solid phase extraction (SPE) methods, respectively. The synthesized IL/ZnO NPs was characterized by FT-IR, SEM, XRD, XPS, and DLS techniques. The optimum conditions were experimentally determined by varying the parameters such as feed concentration, contact time, adsorbent dosage, pH, and temperature using both the adsorbents. From the optimum conditions, it was found that the feed concentration is 10 ppm, contact time is 120 min, adsorbent dosage is 0.2 g, pH is 6, and temperature is 60 °C with the maximum percentage removal of 81% for ZnO Nps, whereas, for IL/ZnO NPs, the feed concentration is 10 ppm, contact time is 90 min, adsorbent dosage is 0.1 g, pH is 6, and temperature is 60 °C with the maximum percentage removal of 92.5%. On comparison with the results, IL/ZnO NPs was an efficient adsorbent for the removal of nickel from aqueous solution as well as the effluents of electroplating and stainless steel industries. The percentage removal of nickel was analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES). The sorbents were regenerated and reused effectively.

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.

Bioconversion of kitchen wastes into bioflocculant and its pilot-scale application in treating iron mineral processing wastewater

In this study, the feasibility of converting kitchen waste into bioflocculant using Bacillus agaradhaerens C9 was analyzed. The result showed that strain C9 could secrete various degrading enzymes, including amylase, protease, lipase, cellulase, xylanase and pectinase, promoting the hydrolysis of kitchen waste. Strong alkaline fermentation condition was able to induce the bioflocculant production, and inhibit the growth of contaminated bacteria, which avoids the sterilization process of kitchen waste. The optimum fermentation condition for enzymatic hydrolysis and bioflocculant production was 40 g/L kitchen waste, 37 °C, pH 9.5, and the highest bioflocculant yield of 6.92 g/L was achieved. Furthermore, bioflocculant was applied to treat pilot-scale (30 L) of mineral processing wastewater for the first time, and the removal rate of 92.35% was observed when 9 mg/L bioflocculant was added into wastewater. Therefore, this study could promote the resource utilization of kitchen waste and recycling of mineral processing wastewater.

Pilot-Scale Removal of Arsenic and Heavy Metals from Mining Wastewater Using Adsorption Combined with Constructed Wetland

This study was conducted to assess the removal of arsenic (As) and heavy metals from mining wastewater by the combination of adsorption, using modified iron-ore drainage sludge, and horizontal-subsurface-flow constructed wetland with common reed (Phragmites australis). The pilot-scale experiment with a constant flow rate of 5 m3/day was operated for four months using real wastewater from a Pb–Zn mine in northern Vietnam. Atomic absorption spectroscopy was used for elemental analysis in wastewater and plant. X-ray diffraction (XRD), surface charge measurements (by a particle charge detector (PCD)), Fourier-transform infrared (FTIR), and surface area Brunauer–Emmet–Teller (BET) measurements were performed to determine the characteristics of the adsorbent. The results showed that the average removals of As, Mn, Cd, Zn, and Pb by the combined system with limestone substrate during four months were 80.3%, 96.9%, 79.6%, 52.9%, and 38.7%, respectively. The use of another constructed wetland substrate, laterite, demonstrated better removal efficiency of As than limestone. The concentrations of As and heavy metals in the effluent were lower than the limits established by the QCVN 40:2011/BTNMT for industrial wastewater, which indicated the feasibility of combining adsorption and constructed wetland for the treatment of mining wastewater.

Preparation of a novel magnetic Pd(II) ion-imprinted polymer for the fast and selective adsorption of palladium ions from aqueous solutions

A novel magnetic ion-imprinted polymer with high accessibility to palladium ions was synthesized via co-precipitation polymerization. Accordingly, a ternary complex composed of PdCl₂ as an imprinting ion, 8-aminoquinoline (AQ) as a ligand, and 4-vinyl pyridine (4-VP) as a complexing monomer was applied to Fe₃O₄@SiO₂ as magnetic core, followed by precipitation polymerization using 2-hydroxyethyl methacrylate (2-HEMA) as a co-monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinker, and 2,2-azobisisobutyronitrile (AIBN) as an initiator in the presence of 2-methoxyethanol as a solvent. The palladium ions were leached out by a solution containing 50% (v/v) HCl. The synthesized polymer was characterized physically and morphologically using different techniques. In order to assess the conditions required for adsorption, as well as the selectivity and reusability, batch adsorption experiments were carried out. The experiments exhibited that the maximum adsorption capacity was about 65.75 mg g^-1 at 25 °C, while the pH solution and the adsorbent dose were 4 and 1 g L^-1, respectively. Kinetic studies of experimental data demonstrated that they correspond very much to the pseudo-second-order kinetic model. The development of the Langmuir and Freundlich isothermal models on the equilibrium data proved to correspond well to the Langmuir isotherm model. Interferences studies of the magnetic polymer demonstrated higher affinity and discernment for palladium ions than other co-existing ions in the solutions. Spontaneous (ΔG < 0) and exothermic (ΔH < 0) behavior of the adsorption process is confirmed by thermodynamic studies. In addition, the affinity of the spent polymer has not been dramatically reduced over at least five regeneration cycles.

Effective Factor Analysis for Chromium(VI) Removal from Aqueous Solutions and Its Application to Tunçbilek Lignite Using Design of Experiments

Poisonous heavy metals in air, water, and soil produce global environmental problems that are considerable threats to humankind. To meet the local and international guidelines for heavy metal release, companies often use different approaches, such as chemical precipitation, chelating agents, or activated carbon produced by adsorption. One of these heavy and toxic metals is chromium(VI). Chromium(VI) is commonly used in many applications, such as dye fixation in the textile industry or as an anticorrosive agent in paints. The aim of this paper is to explore the factors affecting the removal of one of these deadly heavy metals, chromium(VI), from aqueous solutions. For this purpose, activated carbon from Turkish Tunçbilek lignite is prepared with both chemical and physical activation methods to investigate the adsorption behavior of chromium(VI). The effects of initial chromium(VI) concentration, adsorption temperature, and pH on adsorption are studied using a design of experiments method with a full 24 factorial design with center points. The Freundlich and Langmuir adsorption isotherms that are commonly used in chemical engineering are also applied both for predicting the amount of chromium(VI) adsorbed and confirming the validity and advantages of the obtained regression model. The results indicate that the design of experiments and regression can explain and support the design of new materials by using linear and physically meaningful equations instead of local nonlinear and empirical models that are usually insufficient. Additionally, three experiments were carried out in the liquid phase to test the activated carbon samples: chromium, chromium and sucrose, and chromium-sucrose-ion. A change in adsorption capacities of the activated carbon samples was observed. Sucrose was chosen for the experiments because it contains six carbon atoms in a slightly soluble structure. The results indicated that Tunçbilek lignite exhibits good adsorption capability.

Thermodynamic and kinetic insights into plant-mediated detoxification of lead, cadmium, and chromium from aqueous solutions by chemically modified Salvia moorcroftiana leaves

Thermodynamic and kinetic aspects for the biosorptive removal of Pb, Cd, and Cr metals from water using Chemically Modified Leaves of Salvia moorcroftiana (CMSML) were determined. Different parameters including pH, temperature, metal's initial concentration, biomass dosage, and contact time were optimized. Optimum biosorptions of Pb, Cd, and Cr were attained at pH values of 6.0, 7.0, and 3.0 respectively. Batch experiments showed maximum removal of both Pb and Cd at 40 °C and that of Cr at 30 °C. Biosorption capability of CMSML was observed to decrease with raising temperature. Optimal equilibrium times for Pb, Cd, and Cr uptake were 120, 60, and 120 min respectively. Based on the values of regression correlation coefficients (R²), the current data is explained better by applying Langmuir isotherms than the Freundlich model. Maximum biosorbent capabilities (q_max) for Pb, Cd, and Cr were approximately 270.27, 100.00, and 93.45 mg/g respectively. Thermodynamically, removal of all the three metal ions was shown to be exothermic and spontaneous.

Adsorption of Arsenic and Heavy Metals from Solutions by Unmodified Iron-Ore Sludge

Arsenic and heavy-metal-contaminated environments are a major concern due to their negative impacts on exposed people and ecosystems. In this study, sludge from an iron-ore processing area was used as an adsorbent to remove As, Mn, Zn, Cd, and Pb from aqueous solutions. The adsorption capacity of target adsorbates was investigated in batch experiments of both single- and mixed-metal solutions. The batch studies show that the maximum Langmuir adsorption capacities of the heavy metals onto the adsorbent occurred in the order Pb > As > Cd > Zn > Mn, and ranged from 0.710 mg/g to 1.113 mg/g in the single-metal solutions and from 0.370 mg/g to 1.059 mg/g in the mixed-metal solutions. The results of the kinetic experiments are consistent with pseudo-first-order and pseudo-second-order models, with a slightly better fit to the latter. Adsorption performances indicate that iron-ore sludge can simultaneously adsorb multiple metal ions and is a promising adsorbent for the removal of toxic pollutants from water.

Hydrothermal synthesis of a magnetic adsorbent from wasted iron mud for effective removal of heavy metals from smelting wastewater

A magnetic adsorbent (MA) was synthesized from wasted iron mud of a groundwater treatment plant using a novel one-step hydrothermal method. The results showed that Fe content of MA was 41.8 wt%, 2.5 times higher than that of iron mud, which was caused by hydrothermal dissolution of non-ferrous impurities under alkaline condition, such as quartz and albite, regardless of addition of ascorbic acid or not. Ferrihydrite was 92.7% in dry iron mud before adding ascorbic acid and gradually decreased to 58.1% by increasing the molar ratio of ascorbic acid to Fe following hydrothermal treatment. The strongest saturation magnetization of 16.29 emu/g was observed in the prepared MA-4 when the ascorbic acid to Fe molar ratio was 1. The highest surface site concentration of 1.31 mmol/g was observed in MA-2 when the ratio was 0.02. The mechanism of hydrothermal conversion of wasted iron mud to MA was reductive dissolution of ferrihydrite to form siderite, which was then reoxidized to maghemite. When 12.5 g/L of MA-2 was applied to treat smelting wastewater, over 99% removal of Cu²⁺, Zn²⁺, Pb²⁺, and Cd²⁺ was achieved. The major mechanisms of Cu²⁺ and Zn²⁺ adsorption by the adsorbent were cationic exchange.

Surface interactions of Cs+ and Co2+ with bentonite

Uptake of radioactive metal species from soils and solutions by clay particles could be a treatment option due to simplicity of operation and economic cost. In this concern, adsorption behavior of Cs⁺ or Co²⁺ onto bentonite as a function of contact time, pH, initial metal concentration, ionic strength, and temperature was studied by batch adsorption technique. Adsorption isotherm data were interpreted by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Bentonite exhibited maximum adsorption capacity of 83.3 mg g^-1 for Cs⁺ and 15.9 mg g^-1 for Co²⁺. Presence of humic acid (HA) as a representative model of organic matter did not significantly affect the adsorption capacity of bentonite for Cs⁺, whereas it increased the adsorption capacity of bentonite for Co²⁺. Thermodynamic parameters, standard enthalpy (ΔH°), standard entropy (ΔS°), and standard free energy (ΔG°) were determined through batch adsorption experiments performed at four different temperatures of 288, 298, 318, and 338 K. Co²⁺ adsorption onto bentonite showed an endothermic reaction (ΔH° = 13.6 kJ mol^-1) whereas Cs⁺ adsorption displayed an exothermic nature (ΔH° = -4.65 kJ mol^-1). Negative values of ΔG° and positive values of ΔS° indicated the feasibility and spontaneous nature of adsorption processes and more disordered form after adsorption.

Insights into doxycycline adsorption onto graphene nanosheet: a combined quantum mechanics, thermodynamics, and kinetic study

Recently, pharmaceutically active compounds including antibiotics have been detected in drinking water at very low levels, mostly nanogram/liter concentrations, proposing that these materials were unaffected by water treatment processes. Adsorption processes were suggested to play a significant role in the removal of antibiotics. In this study, the adsorption behavior of doxycycline (DC) in aqueous solution was evaluated. The four factors influencing the adsorption of DC onto graphene nanosheet (GNS) were studied. The results showed that initial pH ∼ 6 to 7 and contact time ∼ 200 min are optimum. The monolayer adsorption capacity was reduced with the increasing temperature from 25 to 45 °C. Nonlinear regressions were carried out to define the best fit model for every system. Among various models, the Hill isotherm model represented the equilibrium adsorption data of antibiotics while the kinetic data were well fitted by the Elovich kinetic model. The maximum adsorption capacity (q _max) was 110 mg.g^-1, obtained from the Hill equation. Semiempirical molecular orbital theory was used to investigate the molecular interaction of the adsorption system. The experiments and semiempirical computation have systematically demonstrated that DC could be adsorbed onto GNS by π- π and electrostatic interactions. It was shown that there is a good compromise with the experimental results. Graphical abstract Insights into doxycycline adsorption onto graphene nanosheet: quantum mechanics, thermodynamics, and kinetic study.

Manufacturing of novel low-cost adsorbent: Co-granulation of limestone and coffee waste

Limestone and coffee waste were used during the wet co-granulation process for the production of efficient adsorbents to be used in the removal of anionic and cationic dyes. The adsorbents were characterized using different analytical techniques such as XRD, SEM, FTIR, organic elemental analysis, the nitrogen adsorption method, with wettability, strength and adsorption tests. The adsorption capacity of granules was determined by removal of methylene blue (MB) and orange II (OR) from single and mixed solutions. In the mixed solution, co-granules removed 100% of MB and 85% of OR. The equilibria were established after 6 and 480 h for MB and OR, respectively.

Zeolitic tuffs for acid mine drainage (AMD) treatment in Ecuador: breakthrough curves for Mn2+, Cd2+, Cr3+, Zn2+, and Al3

Zeolitic tuff constitutes a technical and economical feasible alternative to manage acidic waters in initial phases of generation. A study of cation exchange with two zeolitic tuffs from Ecuador and one from Cuba has been conducted using breakthrough curve methodology. Cations Mn²⁺, Cd²⁺, Cr³⁺, Zn²⁺, and Al³⁺ have been chosen owing to their presence in underground water in exploration activities (decline development) in Fruta del Norte (Ecuador). Zeolites characterized by X-ray diffraction and thermal stability after heating overnight as heulandites show a similar exchange behavior for the five cations studied. The clinoptilolite sample Tasajeras shows a relevant cation exchange performance expressed in the important increment of spatial time to reach the breakthrough point in comparison with heulandite samples. The maximum length of unused beds was found for Cr³⁺ and Zn²⁺ cations showing, therefore, a lower adsorption performance in relation with Mn²⁺ and Cd²⁺. A final disposal method of metal-loaded zeolites with cement is proposed.

Simultaneous removal of Ni(II), As(III), and Sb(III) from spiked mine effluent with metakaolin and blast-furnace-slag geopolymers

The mining industry is a major contributor of various toxic metals and metalloids to the aquatic environment. Efficient and economical water treatment methods are therefore of paramount importance. The application of natural or low-cost sorbents has attracted a great deal of interest due to the simplicity of its process and its potential effectiveness. Geopolymers represent an emerging group of sorbents. In this study, blast-furnace-slag and metakaolin geopolymers and their raw materials were tested for simultaneous removal of Ni(II), As(III) and Sb(III) from spiked mine effluent. Blast-furnace-slag geopolymer proved to be the most efficient of the studied materials: the experimental maximum sorption capacities for Ni, As and, Sb were 3.74 mg/g, 0.52 mg/g, and 0.34 mg/g, respectively. Although the capacities were relatively low due to the difficult water matrix, 90-100% removal of Ni, As, and Sb was achieved when the dose of sorbent was increased appropriately. Removal kinetics fitted well with the pseudo-second-order model. Our results indicate that geopolymer technology could offer a simple and effective way to turn blast-furnace slag to an effective sorbent with a specific utilization prospect in the mining industry.

Optimization of process parameters for pilot-scale liquid-state bioconversion of sewage sludge by mixed fungal inoculation

Liquid-state bioconversion (LSB) technique has great potential for application in bioremediation of sewage sludge. The purpose of this study is to determine the optimum level of LSB process of sewage sludge treatment by mixed fungal (Aspergillus niger and Penicillium corylophilum) inoculation in a pilot-scale bioreactor. The optimization of process factors was investigated using response surface methodology based on Box-Behnken design considering hydraulic retention time (HRT) and substrate influent concentration (S0) on nine responses for optimizing and fitted to the regression model. The optimum region was successfully depicted by optimized conditions, which was identified as the best fit for convenient multiple responses. The results from process verification were in close agreement with those obtained through predictions. Considering five runs of different conditions of HRT (low, medium and high 3.62, 6.13 and 8.27 days, respectively) with the range of S0 value (the highest 12.56 and the lowest 7.85 g L(-1)), it was monitored as the lower HRT was considered as the best option because it required minimum days of treatment than the others with influent concentration around 10 g L(-1). Therefore, optimum process factors of 3.62 days for HRT and 10.12 g L(-1) for S0 were identified as the best fit for LSB process and its performance was deviated by less than 5% in most of the cases compared to the predicted values. The recorded optimized results address a dynamic development in commercial-scale biological treatment of wastewater for safe and environment-friendly disposal in near future.

Filter materials for metal removal from mine drainage--a review

A large number of filter materials, organic and inorganic, for removal of heavy metals in mine drainage have been reviewed. Bark, chitin, chitosan, commercial ion exchangers, dairy manure compost, lignite, peat, rice husks, vegetal compost, and yeast are examples of organic materials, while bio-carbons, calcareous shale, dolomite, fly ash, limestone, olivine, steel slag materials and zeolites are examples of inorganic materials. The majority of these filter materials have been investigated in laboratory studies, based on various experimental set-ups (batch and/or column tests) and different conditions. A few materials, for instance steel slag materials, have also been subjects to field investigations under real-life conditions. The results from these investigations show that steel slag materials have the potential to remove heavy metals under different conditions. Ion exchange has been suggested as the major metal removal mechanisms not only for steel slag but also for lignite. Other suggested removal mechanisms have also been identified. Adsorption has been suggested important for activated carbon, precipitation for chitosan and sulphate reduction for olivine. General findings indicate that the results with regard to metal removal vary due to experimental set ups, composition of mine drainage and properties of filter materials and the discrepancies between studies renders normalisation of data difficult. However, the literature reveals that Fe, Zn, Pb, Hg and Al are removed to a large extent. Further investigations, especially under real-life conditions, are however necessary in order to find suitable filter materials for treatment of mine drainage.

Removal of dichloromethane from ground and wastewater: a review

Dichloromethane (DCM) is a toxic volatile compound which is found in the ground waters and wastewaters of the pharmaceutical, chemical, textile, metal-working and petroleum industries. DCM inhibits the growth of aquatic organisms, induces cancer in animals and is potentially carcinogenic for humans. This article aims to review existing water treatments for DCM removal, focusing on recent technological advances. Air stripping, adsorption and pervaporation were found to be effective in separating DCM from water with a process efficiency of about 99%, 90% and 80% respectively. Electrocatalysis over Cu-impregnated carbon fiber electrode, photo irradiation over TiO₂ and photo-Fenton process led to the complete decomposition of DCM. Aerobic and anaerobic water treatment achieved 99% and 95% removal of DCM respectively. The maximum efficiencies observed for acoustic cavitation, radiolysis and catalytic degradation of CH₂Cl₂ were 90%, 92% and 99% respectively. Ozonation and persulfate oxidation showed lower DCM degradation efficiencies, not exceeding 20%. Further combination of different water treatment methods will further increase DCM degradation efficiency.