Near-complete recycling of real mix electroplating sludge as valuable metals via Fe/Cr co-crystallization and stepwise extraction route.

In electroplating sludge, iron (Fe) and aluminum (Al) are common impurities that need to be separated before recycling valuable heavy metals. However, the traditional Fe/Al separation process often leads to significant losses of heavy metals. To address this issue, a new approach was developed to sequentially separate Fe/Al and recycle chromium (Cr) and nickel (Ni) from real electroplating sludge. The sludge contained 4.5% Cr, 1.2% Al, 1.1% Ni, and 14.6% Fe. Initially, the sludge was completely dissolved in a mixture of hydrochloric and nitric acids. The resulting acid solution was then heated to 160 °C for 10 h with the addition of saccharose. This hydrothermal treatment led to the hydrolysis and crystallization of 98.3% of Fe, 31.8% of Cr, 1.1% of Al, and 4.9% of Ni, forming akaganeite-bearing particles. It was observed that the excessive amount of saccharose also improved the removal of Cr, Al, and Ni, but decreased the removal of Fe. After the hydrothermal treatment, the remaining supernatant was adjusted to different pH levels (1.9, 2.9, and 4.5, respectively), and then Al, Cr, and Ni were stepwise extracted using di-(2-ethylhexyl) phosphate acid (P204). The recycling efficiencies achieved were 97.4% for Al, 61.2% for Cr, and 89.3% for Ni. This approach provides a promising method for the stepwise separation of Fe/Al and the recycling of heavy metals from electroplating sludge.

In-situ generation of iron activated percarbonate for sustainable sludge dewatering.

Effective dewatering of sewage sludge could potentially address the issues of high energy consumption and large carbon footprint inherent in the sludge treatment process, advancing toward carbon neutrality in environmental remediation. Yet, the surface hydrophilic characteristics and water-holding interfacial affinity in sludge led to dwindled sludge-water separation performance. Here, the integration of in-situ generation of iron from zero-valent scrap iron (ZVSI) and sodium percarbonate (SPC) was attempted to attenuate the water-retaining interfacial affinity within sludge, thus achieving superior sludge dewatering performance. Results showed that under the optimal conditions, the ZVSI + SPC system led to a remarkable decline of 76.09 % in the specific resistance to filtration of the sludge, accompanied by a notable decline of 34.96 % in the water content. Moreover, the utilization of ZVSI + SPC system could be a viable alternative to the traditional strategies in terms of enhanced sludge dewaterability, offering application potential with stable operating performance, economic feasibility, and reduced carbon emissions. Investigation into dewatering mechanism revealed that ZVSI could maintain the Fe3+/Fe2+ in a stable dynamic cycle and continuously in-situ generate Fe2+, thereby efficaciously fostering the SPC activation for the ceaseless yield of reactive oxygen species. The predominant •OH and 1O2 efficiently decomposed the hydrophilic biopolymers, therefore minimizing the hydrophilic protein secondary structures, along with the hydrogen and disulfide bonds within proteins. Subsequently, the water-holding interfacial affinity was profoundly diminished, leading to intensified hydrophobicity, self-flocculation, and dewaterability. These findings have important implications for the advancement of efficacious ZVSI + SPC conditioning techniques toward sustainable energy and low-carbon prospects.

Effect of inorganic anions on hydrothermal removal of impurities Fe/Al from Cu-bearing polymetallic leachate.

Hydrometallurgy recycling of heavy metals from electroplating sludge is of hot spot in recent decades. Such recycling was tedious in the separation of impure Fe/Al prior to heavy metals from acid leachate after sludge dissolution. Herein, a facile hydrothermal route was developed to separate Fe/Al from Cu-bearing leachate. The results showed that when the leachate was directly hydrothermally treated at 160 °C in the presence of nitrate and ethanol, Al/Cu were stable in the leachate, but nearly 100% Fe was removed as hematite nanoparticles. With the addition of chloridion, the removal efficiencies of Fe/Al/Cu did not change apparently, but the corresponding precipitate was akageneite, not hematite. By replacing chloridion with sulfate, nearly 100% Fe and 98.6% Al were separated as natrojarosite/natroalunite block, while the Cu loss was only 1.7%. However, with the supplementary of phosphate, the Fe/Al removal achieved nearly 100%, but the Cu removal also achieved by 92.6%. The thermodynamic analysis showed that Cu was precipitated rapidly via the phosphate/Cu oxyhydroxide route by adding phosphate but removed slightly via the coordination route on the Fe/Al precipitates with the addition of nitrate, chloridion, and sulfate. In summary, Fe was effectively separated as hematite, akageneite, natrojarosite, and phosphate halite, in the presence of nitrate, chloridion, sulfate, and phosphate, separately. But the removal of Al as natroalunite and AlPO4 only started by adding sulfate and phosphate, respectively. Such results enabled a short hydrometallurgy process to effectively recycle heavy metals from electroplating sludge.

An entire recycling of spent Al-bearing cathode powder as giniite sphere and lithiophophate plate with leaching-hydrothermal-precipitation process.

Spent lithium battery is a polymetallic waste, and valuable to be recovered as Li-bearing chemical with the barriers of impurities separation, especially Fe and Al. Here in, Li-rich cathode powder was manually disassembled from spent battery, and then recovered as lithiophosphate plate in consideration of effective separation of impure Fe/Al. The powder comprised of 23.2% Fe, 3.2% Al, 5.5% Li and 19.6% P, and then dissolved by azotic acid as Li-rich solution. When the solution was heated to 190°C for 10 h with the supplementary of saccharose, more than 99.9% Fe and 98.9% Al were removed as spherical giniite particles, in accordance with the rest of Fe/Al at the concentrations of 2.1 and 14 mg/L, whilst the loss of Li was less than 1.5%. But without saccharose, the Fe/Al removals only achieved by 99.2% and 52.1%. It is also found that the Fe/Al/Li removal achieved by 99.6%, 96% and 25.3% after adjusting the solution to pH 2.7 by NaOH. After hydrothermal treatment, the rest Li can be recycled as lithiophosphate plate by pH adjustment, in contrast to the recovery efficiency of 98.5% Li. Such method raised a facile route to effectively separate impure Fe/Al from Li-rich cathode powder, and showed promising application in the industrial recovery of spent battery.

Efficient separation of impurities Fe/Al/Ca and recovery of Zn from electroplating sludge using glucose as reductant.

Electroplating sludge (ES), a hazardous waste containing heavy metals and Fe/Al/Ca impurities, is conventionally disposed of in landfills. In this study, a pilot-scale vessel with an effective capacity of 20 L was applied to recycle Zn from real ES. The sludge contained 6.3 wt% Fe, 6.9 wt% Al, 2.6 wt% Si, 6.1 wt% Ca, and 17.6 wt% Zn and was treated using a four-step method. First, ES was dissolved in nitric acid after washing in a water bath at 75 °C for 3 h to produce an acidic solution with Fe, Al, Ca, and Zn concentrations of 4527.2, 3116.1, 3357.7, and 21,275 mg/L, respectively. Second, the acidic solution was added with glucose at an Mglucose/Mnitrate ratio of 0.08 and hydrothermally treated at 160 °C for 4 h. During this step, nearly 100 % Fe and 100 % Al were simultaneously removed as a mixture containing 53.1 wt% Fe2O3 and 45.7 wt% Al2O3. This process was repeated five times, during which the Fe/Al removal and Ca/Zn loss rates remained unchanged. Third, the residual solution was adjusted with sulfuric acid, and over 99 % Ca was removed as gypsum. The residual Fe, Al, Ca, and Zn concentrations were 0.44, 0.88, 52.59, and 31,177.1 mg/L, respectively. Finally, Zn in the solution was precipitated as ZnO with a concentration of 94.3 %. Economic calculations showed that each 1 t of ES processed created revenue of about $122. This is the first study of high-value metal resource recovery using real electroplating sludge at the pilot scale. This work highlights the pilot-scale application of resource utilization of real ES and provides new insights into the recycling of heavy metals from hazardous waste.

Effective recovery of Ti as anatase nanoparticles from waste red mud via a coupled leaching and boiling route.

Red mud (RM) a solid waste generated by the bauxite smelting industry, is a rich source of metal resources, especially Ti, and its recycling can bring significant environmental and economic benefits. In this study, precious metal Ti was efficiently recovered from red mud using a coupled acid leaching and boiling route for the effective separation of low-value metals. The red mud which contained mainly 10.69% Si, 12.1% Al, 15.2% Ca, 10.99% Fe, and 4.37% Ti, was recovered in five steps. First, a nitric acid solution was used to leach the metals in multiple stages, resulting in an acidic leach solution with high concentrations of Fe, Al, Ti, and Ca ions 2.7 g/L, 4.7 g/L, 5.43 g/L, and 1.8 g/L, respectively. Then, a small amount of sucrose was added as a catalyst to recover Ti from the leach solution under hydrothermal conditions, resulting in the targeted recovery of 98.6% of Ti in the form of high-purity anatase while Fe, Al, and Ca remained in the solution. Next, the Fe in solution was separated as hematite products at a temperature of 110°C and a reaction time of 4 h. Similarly, the Al in the solution was separated and precipitated as boehmite by heating it at 260°C for a reaction time of 20 h. Finally, the remaining Ca in solution was recovered by simple pH regulation. Economic accounting assessment showed that the method yields $101.06 for 1 t of red mud treated, excluding labor costs. This study provides a novel approach to recover precious metals from metal wastes through the whole process resource recovery of solid waste red mud.

Valorization of waste Fe-rich sludge as erdite/KFeS2 rods under atmosphere condition and evaluation of their mutual transformation.

Pilot scale production of one-dimensional (FeS2)nn- rods was performed by using an automatic 20 L vessel at 80 °C under atmosphere condition with the resource utilization of Fe-rich sludge. The sludge was simulated at lab-scale with chemical pure of ferric trichloride. After the sludge treatment, the corresponding rods were not formed at room temperature. But by heating at 80 °C, erdite rod was well-crystallized after 0.5 h by only adding Na halite, and KFeS2 rod was crystallized weakly after 2 h and highly at 10 h with the addition of K halite. After 48 h heating, the rods grow radially to 300 nm for erdite, but to 5 µm for KFeS2. However, at room temperature, erdite rod was converted to high crystallized KFeS2 in KOH water or ethanol solution, whilst the conversion of KFeS2 rod to erdite also occurred in NaOH water solution, but terminated in NaOH ethanol solution, without any morphology change. It is also noted that with the presence of both Na and K halite, the rod was an intermediate of erdite to KFeS2 with 1 µm length after heating at 100 °C but converted to 10-µm-length KFeS2 crystal at the temperature of > 120 °C. The thermodynamic results confirmed that during the rod polymerization, the Fe(OH)3HS- formation was the sole rate-limiting step and showed a positive Gibbs value of 6.45 kJ/mol at room temperature and negative values at the temperature of > 48 °C. In summary, this method not only enabled the vaporization of waste Fe-rich sludge as value-added rods without generating any secondary waste but also showed a new route for the in situ conversion of erdite/KFeS2 rods at room temperature.

Effect of transient organic load and aeration changes to pollutant removal and extracellular polymeric substances.

Transient organic load shocks have an important influence on the removal of pollutants and the content and composition of extracellular polymeric substances (EPS). This study was based on a micro-pressure reactor (MPR) with the influent COD concentration as the variable, while different operating conditions were controlled by adjusting the aeration rate. The effect of single-cycle transient organic loading shocks on EPS and pollutant removal and the correlation between their changes were investigated. The results showed that COD removal was unaffected under the shock, and the effect of nitrogen and phosphorus removal decreased. As the incoming carbon source increased, the EPS content at shock increased, with the polysaccharide (PS) content being the most affected. As aeration increased, the effect of organic load shock on EPS and pollutant removal decreased. Under different aeration conditions, PS contributed to denitrification and anaerobic phosphorus release during transient organic load shocks, and protein (PN) contributed to aerobic phosphorus uptake. The reduction in PS and PN relative to the pre-shock caused by the shock resulted in the EPS exhibiting a favourable effect on COD removal and an inhibitory effect on the effectiveness of nitrogen and phosphorus removal.

Comparison of disinfection by-products formed by preoxidation of sulfamethazine by K2FeO4 and O3 and the influence on cytotoxicity and biological toxicity.

This study researched the formation of disinfection by-products (DBPs) in sulfamethazine (SMZ) chlorination after preoxidation by K2FeO4 and O3 and the influence of preoxidation on cytotoxicity and biological toxicity. Then, the study emphatically analyzed the influencing factors such as NaClO dosage, pH value, reaction temperature, fulvic acid (FA), and bromide and iodide ions. The results showed that preoxidation by K2FeO4 effectively inhibited the formation of DBPs of haloketones (HKS) and trihalomethanes (THMs), with an average inhibition rate of over 60%. The formation of DBPs after preoxidation by O3 was higher than that by K2FeO4; preoxidation by K2FeO4 reduced the influence of NaClO dosage, temperature, and pH value on the production of DBPs after SMZ chlorination. The cytotoxicity and biological toxicity of SMZ chlorination after preoxidation were evaluated and compared by calculating the LC50 value of DBPs and the luminescent bacteria method. The results of both calculation methods showed that the toxicity of DBPs after preoxidation by K2FeO4 was lower than that by O3 preoxidation. K2FeO4 and O3 preoxidation improved the SMZ removal efficiency by 8.41 and 10.49%, respectively, and inhibited the formation of most DBPs, but the preoxidation promoted the formation of highly toxic DBPs (HANs). The toxicity of DBPs formed in SMZ chlorination after preoxidation by K2FeO4 and O3 was slightly higher than that of chlorination disinfection alone, but it was still within the safe range. This study provides more new details about the formation and toxicity changes of DBPs in the process of SMZ chlorination after preoxidation.

Electrocatalytic degradation of sulfamethylthiadiazole by GAC@Ni/Fe three-dimensional particle electrode.

In this work, GAC@Ni/Fe particle electrodes were prepared and employed for the degradation of sulfamethylthiadiazole (SMT) by three-dimensional electrocatalytic technology. The effects of particle electrode bi-metal loading ratio, cell voltage, particle electrode dosage, electrode plate spacing, and SMT initial concentration on SMT removal were studied. In addition, GAC@Ni/Fe particle electrode was analyzed by the scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and Fourier transform infrared spectrometer (FTIR) to characterize which indicated that a significant amount of iron-nickel oxide was formed on the surface of GAC@Ni/Fe particle electrode. The results indicated that when the nickel-iron loading ratio is 1:1, the SMT removal effect is the best, and the removal rate can reach 90.89% within 30 min. Compared with the granular activated carbon without bimetal, the removal efficiency is increased by 37.58%. The degradation of SMT in the GAC@Ni/Fe particle three-dimensional electrode reactor is the joint result of both direct oxidation and indirect oxidation. The contribution rates of direct oxidation of anode and particle electrode and indirect oxidation of ·OH in the degradation are 32%, 27%, and 41%, respectively. Based on the intermediate detected by ultra-high liquid chromatography and the calculation of bond energy of SMT molecule by Gauss software, the degradation pathway of SMT in the GAC@Ni/Fe three-dimensional electrode reactor is proposed. This research provides a green, healthy, and effective method for removing sulfonamide micro-polluted wastewater.

Deciphering the influence of multiple anthropogenic inputs on taxonomic and functional profiles of the microbial communities in Yitong River, Northeast China.

We conducted the analysis of physicochemical parameters, 16S rRNA amplicon sequencing and real-time quantitative polymerase chain reaction to explore the impact of human inputs on the bacterioplankton communities within a tributary of the largest river flowing through a megacity in northeast China. Agriculture largely accounted for the alteration of diversity and functions of the microbial communities. Furthermore, nitrate and total phosphorus declined at the reservoir outlet. The WWTP effluent discharge caused a decrease of the relative abundance of Actinobacteria and Cyanobacteria, while the impact on the variation of alpha diversity of river microbial community was slight. Carbon fixation and nitrogen cycle varied with the change of land use type. The rare taxa contributed with a predominant role in the response to environmental variables and NH3-N as well as NO3--N were the main environmental factors that drove the shift in the bacterial community. The occurrence of the human-specific fecal indicator was mostly derived from agriculture, and its increase in relative abundance was observed in the WWTP effluent. Thus, our study provides guidance for ecological assessment and management of rivers by revealing the response pattern of river bacterioplankton to multiple types of anthropogenic stressors.

Nanocrystalline erdite from iron-rich sludge: Green synthesis, characterization and utilization as an efficient adsorbent of hexavalent chromium.

A low-temperature hydrothermal process was developed to synthesize erdite adsorbent from a solid waste sludge contained 10.2% Fe, 6.2% Al and 1.4% Si, alongside 59.5% water content. At 90℃, adding Na2S and NaOH could convert it into erdite nanorods with a diameter of 80 nm and a length of 100 nm. In the sludge, only Fe oxyhydroxide was involved in the formation of erdite, and the other Al/Si-bearing compounds were dissolved in an alkaline medium. The dissolved Al/Si-bearing compounds were further removed, forming faujasite so that the used medium was purified and then entirely recycled into the next conversion stage. No secondary waste was generated in the pilot-scale conversion, and the adsorption efficiency of the prepared products to wastewater with a high initial Cr(VI) concentration of 1000 mg/L was more than 99.5%. The adsorption data complied with the pseudo-second-order kinetics. During the wastewater treatment, hexavalent chromium anion diffused to erdite surface and replaced OH/SH groups of adjacent structural Fe to form a stable complex ligand. In addition, the redox reaction between hexavalent chromium and the -SH group occurred to generate a trivalent chromium complex on the Fe/S-bearing flocs surface.

Stepwise extraction of Fe, Al, Ca, and Zn: A green route to recycle raw electroplating sludge.

Electroplating sludge is a hazardous waste produced in large quantities in the electroplating industry during production. It is rich in heavy metal resources and can be recovered as value-added heavy metal products. To recover Zn in electroplating sludge, Fe/Al/Ca impurities were effectively removed as hematite, boehmite, and calcium sulfate, respectively, via a facile hydrothermal method with reduction of nitric acid by addition of glucose. After the sludge was dissolved in nitric acid, the generated solution contained 6.1 g/L of Zn, 2.2 g/L of Fe, 2.5 g/L of Al, and 2.9 g/L of Ca. First, approximately 100% Fe was extracted as hematite nanoparticles containing 94.6 wt% Fe2O3 after the solution was treated at 190 °C for 6 h. Second, when the temperature was elevated to 270 °C, nearly 99% Al was isolated as boehmite particles containing 95.2 wt% Al2O3. Third, more than 98% Ca was removed as anhydrite, which contained 95.9 wt% CaSO4, by adding sulfuric acid. During the steps, the total loss of Zn was less than 3%, and 5.75 g/L of residual Zn was recovered as zincite containing 92.2 wt% ZnO by adjusting the pH to 8. The dissolved Fe, Al, and Ca impurities were successfully removed as purified hematite, boehmite, and anhydrite, respectively, through the stepwise separation method by adjusting reaction temperatures and pH. The high content of Zn in the electroplating sludge was finally purified as zincite.

Synthesis of novel erdite nanorods for the activation of peroxymonosulfate during p-nitrophenol wastewater treatment.

Fe-bearing salt and minerals are common reagents used in activating peroxymonosulfate (PMS) for Fenton-like oxidation in wastewater treatment. Fe-bearing reagents are used in mass production, which generate abundant Fe-bearing waste sludge in the absence of a reductant for Fe3+/Fe2+ cycling. Herein, a novel Fe/S-bearing mineral, erdite, was synthesized with a one-step hydrothermal route. The material exerted an Fe/S synergetic effect for p-nitrophenol degradation upon PMS activation and showed a one-dimensional structure similar to that of (FeS2)nn-. It contained short rods with diameters of 100 nm and lengths ranging from 200 to 400 nm. It grew radically to 0.8-2 µm in length upon the addition of MnO2. Ps-0.5, prepared by adding MnO2 in an Mn/Fe molar ratio of 0.5, showed optimal efficiency in removing approximately 99.4% of p-nitrophenol upon PMS activation. Only 3.3% of p-nitrophenol was removed without MnO2. The efficiency of p-nitrophenol removal through Ps-0.5 activation was higher than that through FeSO4, nanoscale zero-valent iron (nZVI), CuFeS2, and MnSO4 activation. The formed erdite rods were spontaneously hydrolyzed to Fe/S-bearing flocs, in which an electron was used by structural S to reduce Fe3+ to Fe2+ upon PMS activation. The reduction resulted in a high p-nitrophenol removal rate. This study provided new insight into the development of an effective PMS activator in wastewater treatment.

Resource Recycling of Mn-Rich Sludge: Effective Separation of Impure Fe/Al and Recovery of High-Purity Hausmannite.

Groundwater treatment sludge is a Fe/Mn-rich waste generated in mass production in a groundwater treatment plant for potable water production. The conventional disposal of sludge, such as direct discharge into river/lake, sea, and landfill, is not environmentally sustainable. Herein, a novel method was proposed to effectively separate Fe/Al and recover Mn via a combined hydrochloric acid leaching and hydrothermal route. The sludge contained 14.6% Fe, 6.3% Mn, and 11.5% Al and was first dissolved in 5 M HCl to prepare a leaching solution. Second, the leaching solution was hydrothermally treated, in which 97.1% Fe and 94.8% Al were precipitated as hematite and boehmite and more than 98% Mn was kept. Increasing the reaction temperature to 270 °C was beneficial for Fe/Al removal. With the consumption of abundant H+, the reaction of added glucose and nitrate accelerated as the temperature increased. An optimal pH was utilized for Fe/Al hydrolysis and crystallization, leading to extensive removal of Fe/Al. Third, the residual solution was adjusted to pH 8.3 with NaOH, and approximately, 99.2% Mn was removed as hausmannite with a Mn content of 63.6%. This method exhibited efficient separation of impure Fe/Al from Mn-rich groundwater treatment plant iron mud, and the recycled high-purity hausmannite was a marketable active pharmaceutical ingredient.

Pilot study on urban sewage treatment with micro pressure swirl reactor.

This study aimed to propose a new type of micro-pressure swirl reactor (MPSR) to treat urban sewage. The MPSR could form a stable swirl in the reactor, and realized the coexistence of anaerobic, anoxic, and aerobic zones in a single aeration tank. The pilot study showed that MPSR achieved high removal efficient of SS, COD, NH4+-N, TN, TP under the conditions of drastic fluctuation in influent quality and temperature, and the average removal rate were 88.58%, 93.32%, 94.47%, 73.19%, 96.16%. The relative high abundance of Thermomonas, Thaurea, and Dechloromonas, etc, guaranteed the denitrification efficiency of the MPSR, and Dechloromonas was the main phosphorus removal bacteria in the system. The study confirmed the rationality of the structural design of the MPSR, and it was excellent in sewage treatment and stability.

Micro-pressure swirl reactor (MPSR) for efficient COD and nitrogen removal of high-concentration wastewater.

A micro-pressure swirl reactor (MPSR) was developed for carbon and nitrogen removal of wastewater, in which dissolved oxygen (DO) gradient and internal circulation could be created by setting the aerators along one side of the reactor, and micro-pressure could be realized by sealing most of the top cap and increasing the outlet water level. In this study, velocity and DO distribution in the reactor was measured, removal performance treating high-concentration wastewater was investigated, and the main functional microorganisms were analyzed. The experiment results indicated that there was stable swirl flow and spatial DO gradient in MPSR. Operated in sequencing batch reactor mode, distinct biological environments spatially and temporally were created. Under the average influent condition of chemical oxygen demand (COD) concentration of 2,884 mg/L and total nitrogen (TN) of 184 mg/L, COD removal efficiency and removal loading was 98% and 1.8 kgCOD/(m3·d) respectively, and TN removal efficiency and removal loading reached up to 90% and 0.11 kgTN/(m3·d) respectively. With efficient utilization of DO and simpler configuration for simultaneous nitrification and denitrification, the MPSR has the potential of treating high-concentration wastewater at lower cost.

Upcycling of Fe-bearing sludge: preparation of erdite-bearing particles for treating pharmaceutical manufacture wastewater.

Groundwater treatment sludge is a type of solid waste with 9.0-28.9% wt.% Fe content and is precipitated in large quantity from backwash wastewater in groundwater treatment. The sludge is mainly composed of fine particles containing Fe, Si and Al oxides, such as ferrihydrite, quartz and boehmite. The Fe oxides mostly originate from the oxidation of ferrous Fe in groundwater, whilst the silicate/aluminium compounds mainly originate from the broken quartz sand filter in the backwash step. In general, the sludge is firstly coagulated, dewatered by filter pressing and finally undergoes harmless solidification before it is sent to landfills. However, this process is costly (approximately US$66.1/t) and complicated. In this study, groundwater treatment sludge was effectively recycled to prepare novel erdite-bearing particles via a one-step hydrothermal method by adding only Na2S·9H2O. After hydrothermal treatment, the quartz and boehmite of the sludge were dissolved and recrystallised to sodalite, whilst ferrihydrite was converted to an erdite nanorod at 160 °C and a hematite at 240 °C. SP160 was prepared as fine nanorod particles with 200 nm diameter and 2-5 µm length at a hydrothermal temperature of 160 °C. Nearly 100% OTC and its derivatives in pharmaceutical manufacture wastewater were removed by adding 0.1 g SP160. The major mechanism for the removal was the spontaneous hydrolysis of erdite in SP160 to generate Fe oxyhydroxide and use many hydroxyl groups for coordinating OTC and its derivatives. This study presents a novel method for the resource reutilisation of waste groundwater treatment sludge and reports efficient erdite-bearing particles for pharmaceutical manufacture wastewater treatment.

Effective recycling of Cu from electroplating wastewater effluent via the combined Fenton oxidation and hydrometallurgy route.

Heavy metals, which commonly occur in complex forms, are difficult to remove in alkali electroplating wastewater effluent, and their resource recycling is rarely reported. Here, a Cu-bearing alkali wastewater effluent was effectively treated through Fenton oxidation, and the generated Fenton sludge was recycled into highly pure tenorite and hematite particles. The effluent contained 1.51 mg/L Cu and was subjected to Fenton oxidation, pH adjustment and coagulation. Amongst the three methods, Fenton oxidation showed superior efficiency to Cu removal, and the residual Cu in the effluent was 0.06 mg/L, thereby meeting the discharge standard for electroplating wastewater. However, Cu removal achieved less than 20% after pH adjustment and coagulation. Cu-bearing sludge, which was generated through the Fenton process, was dissolved in a mixture of hydrochloric and nitric acids. The dissolved solution contained 1.92 g/L Cu and 73.6 g/L Fe impurity. Impure Fe (67.4%) was removed as hematite aggregates after the solution was directly treated via a hydrometallurgy route, whilst 99.2% Cu was kept. When 0.5 mL of methanol was introduced to the hydrometallurgy system, nearly 100% Fe was removed as hematite nanoparticles with 94.8% purity, whilst more than 98% Cu was kept. The residual Cu was 1.88 g/L and precipitated as a tenorite block with a CuO content of 91.1% by adjusting the treated solution to pH 9. This study presented an environment-friendly method for enriching Cu from electroplating wastewater effluent without generating any waste.

Upcycling of groundwater treatment sludge to magnetic Fe/Mn-bearing nanorod for chromate adsorption from wastewater treatment.

Groundwater treatment sludge is a Fe/Mn-bearing waste that is mass produced in groundwater treatment plant. In this study, sludge was converted to a magnetic adsorbent (MA) by adding ascorbate. The sludge was weakly magnetised in the amorphous form with Fe and Mn contents of 28.8% and 8.1%, respectively. After hydrothermal treatment, Fe/Mn oxides in the sludge was recrystallised to siderite and rhodochrosite, with jacobsite as the intermediate in the presence of ascorbate. With an increment in ascorbate dosage, the obtained magnetic adsorbent had a significant increase in chromate adsorption but a decrease in magnetisation. When the Mascorbate/MFe molar ratio was 10, the produced MA-10 was a dumbbell-shaped nanorod with a length of 2-5 µm and a diameter of 0.5-1 µm. This MA-10 showed 183.2 mg/g of chromate adsorption capacity and 2.81 emu/g of magnetisation. The mechanism of chromate adsorption was surface coprecipitation of the generated Cr3+ and Fe3+/Mn4+ from redox reaction between chromate and siderite/rhodochrosite on MA-10, separately. This study demonstrated an efficient recycling route of waste sludge from groundwater treatment to produce MA for treating chromate-bearing wastewater.