Plating Wastewater Research Articles

TOXICITY IDENTIFICATION AND CONFIRMATION OF METAL PLATTING WASTEWATER

Toxicity of metal plating wastewater was evaluated by using acute toxicity tests on Daphnia magna. To identify toxicants of metal plating wastewater, several manipulations such as solid phase extraction (SPE), ion exchange and graduated pH adjustment were used. The SPE test had no significant effect on baseline toxicity, suggesting absence of toxic non-polar organics in metal plating wastewater. However, anion exchange largely decreased the baseline toxicity by 88%, indicating the causative toxicants were inorganic anions. Considering high concentration of chromium in metal plating wastewater, it is thought the anion is Cr(VI) species. Graduated pH test showing independence of the toxicity on pH change strongly supports this assumption. However, as revealed by toxicity confirmation experiment, the initial toxicity of metal plating wastewater (24-h TU=435) was not explained only by Cr(VI) (24-h TU = 725 at ). Addition of nickel() and copper () largely decreased the chromium toxicity up to 417 TU, indicating antagonistic interaction between heavy metals. This heavy metal interaction was successfully predicted by an equation of 24-h at a fixed concentration of chromium.

Preparation of silica-supported porous sorbent for heavy metal ions removal in wastewater treatment by organic–inorganic hybridization combined with sucrose and polyethylene glycol imprinting

A new porous sorbent for wastewater treatment of metal ions was synthesized by covalent grafting of molecularly imprinted organic–inorganic hybrid on silica gel. With sucrose and polyethylene glycol 4000 (PEG 4000) being synergic imprinting molecules, covalent surface coating on silica gel was achieved by using polysaccharide-incorporated sol–gel process starting from the functional biopolymer, chitosan and an inorganic epoxy-precursor, gamma-glycidoxypropyltrimethoxysiloxane (GPTMS) at room temperature. The prepared porous sorbent was characterized by using simultaneous thermogravimetry and differential scanning calorimeter (TG/DSC), scanning electron microscopy (SEM), nitrogen adsorption porosimetry measurement and X-ray diffraction (XRD). Copper ion, Cu 2+, was chosen as the model metal ion to evaluate the effectiveness of the new biosorbent in wastewater treatment. The influence of epoxy-siloxane dose, buffer pH and co-existed ions on Cu 2+ adsorption was assessed through batch experiments. The imprinted composite sorbent offered a fast kinetics for the adsorption of Cu 2+. The uptake capacity of the sorbent imprinted by two pore-building components was higher than those imprinted with only a single component. The dynamic adsorption in column underwent a good elimination of Cu 2+ in treating electric plating wastewater. The prepared composite sorbent exhibited high reusability. Easy preparation of the described porous composite sorbent, absence of organic solvents, cost-effectiveness and high stability make this approach attractive in biosorption.

Di(2-ethylhexyl)phosphoric acid-coconut oil supported liquid membrane for the separation of copper ions from copper plating wastewater

Permeation of Cu(II) from its aqueous solution through a supported liquid membrane (SLM) containing di(2-ethylhexyl)phosphoric acid (D2EHPA) carrier dissolved in coconut oil has been studied. The effects of Cu(II), pH (in feed), H 2SO 4 (stripping) and D2EHPA (in membrane) concentrations have been investigated. The stability of the D2EHPA-coconut oil has also been evaluated. High Cu(II) concentration in the feed leads to an increase in flux from 4.1 × 10 −9 to 8.9 × 10 −9 mol/(m2·s) within the Cu(II) concentration range 7.8×10 −4 −78.6×10 −4 mol/L at pH of 4.0 in the feed and 12.4 × 10 −4 mol/L D2EHPA in the membrane phase. Increase in H 2SO 4 concentration in strip solution leads to an increase in copper ions flux up to 0.25 mol/LH 2SO 4, providing a maximum flux of 7.4 × 10 −9 mol/(m 2·s). The optimum conditions for Cu(II) transport are, pH of feed 4.0, 0.25 mol/LH 2SO 4 in strip phase and 12.4 × 10 −4 mol/L D2EHPA (membrane) in 0.5 μm pore size polytetrafluoroethylene (PTFE) membrane. It has been observed that Cu(II) flux across the membrane tends to increase with the concentration of copper ions. Application of the method developed to copper plating bath rinse solutions has been found to be successful in the recovery of Cu(II).

Rapid gold ion recovery from wastewater by photocatalytic ZnO nanopowders

In this study, ZnO nanopowder was synthesized by solution-combustion method (SCM). The photocatalytic gold recovery efficiency by this SCM ZnO nanopowder was about 6 fold higher compared to the case by the state of the art commercial TiO2 nanopowder. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Furthermore, the ZnO nanopowder synthesis method and gold recovery process are very cost-effective. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating wastewater. This technology is therefore very viable to obtain high purity gold from plating wastewater.

Synthesis of Solution-Combusted ZnO Nanopowder and Its Application to Gold Recovery

Photocatlytic ZnO nanopowders were synthesized by a novel method referred to as “solution-combustion method (SCM)”. They were synthesized using various oxidants and fuels. Single-phase ZnO powders were obtained. The ZnO powder synthesized using Zn(OH)2 and glycine as an oxidant and a fuel at fuel/oxidant ratio of 0.8, showed best powder characteristics such as average grain size of 30 nm and the specific surface area of 120 m2/g. The photocatalytic gold recovery efficiency by this SCM ZnO nanopowders was about 6 fold higher compared to the case by the state of the art commercial TiO2 nanopowders. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating one. This technology is therefore very viable and cost-effective to obtain high purity gold from plating wastewater.

Optimum pH for Cr6+ Co-removal with Mixed Cu2+, Zn2+, and Ni2+ Precipitation

It is advisable to co-remove Cr(VI) with available Cu(II), Zn(II), and Ni(II) since they coexist in most plating wastewater. Previous studies showed that coprecipitation and adsorption are the main mechanisms contributable to Cr(VI) co-removal with Cu(II) precipitation, and both are highly pH dependent. This study presents the effect of pH on Cr(VI) co-removal with mixed metal precipitation in batch tests and also in a continuous compact system. Batch tests indicate that a maximum of 46.8 mg L -1 Cr(VI) was co-removed with the precipitation of Cu(II), Zn(II), and Ni(II), each 150 mg L -1 , at pH of 7.0-7.3. However, co-removal of Cr(VI) decreased significantly with further pH increasing. Therefore in the continuous system, a two-stage nucleated precipitation technology was designed with the first stage being operated at around pH 7.2 to obtain maximum Cr(VI) co-removal and the second stage at around pH 9.2 to achieve further Cr(VI) co-removal with Zn(II) and Ni(II) precipitation.

Towards a “crippled-mode” operation of an industrial wastewater treatment plant

In house treatment of metal plating wastewater mainly involves chemical treatments performed in continuous flow stirred tank reactors (CFSTR). The inflow of these tanks is directly produced by the plating shops activity, and the storage capacity never exceeds a few hours of incoming flow. Thus, any fault on one of the CFSTR may impose a complete stop of the whole manufacturing process, which is unacceptable for the manufacturer. Another solution would be having "spare" CFSTRs ready to be used as alternative in case of any CFSTR fault or maintenance. The latter solution however implies additional costs in equipment, storage space and maintenance so as to keep this equipment fit and ready for operation. The paper presents the study of a "crippled-mode" wastewater treatment (WWT) operation which enables a sufficiently efficient working of the WWT plant during maintenance phases and failure repairing on any of the CFSTR, without any extra equipment needed. This survey has been performed on real industrial WWT plants, with a continuous influent and under industrial operation constraints. The performances of the detoxication have been analysed when a CFSTR is short-circuited and the corresponding chemical treatment is shunt in the upstream or downstream CSFTR. This work shows the possibility of satisfying the environmental regulations with a WWT plant functioning under subnormal conditions.

Performance Evaluation of Pilot Scale Sulfur-Oxidizing Denitrification for Treatment of Metal Plating Wastewater

A full-scale and two pilot-scale upflow sulfur-oxidizing denitrification (SOD) columns were evaluated using metal plating wastewater as feed. The sludge was autotrophically enriched, and inoculated in the SOD columns attached to the effluent line of three metal plating wastewater treatment facilities. The effects of activated carbon and aeration were also studied, and found effective for the removal of suspended solids and ammonia, respectively. The results showed that the constituents, such as the total nitrogen, nitrates, nitrites, ammonia, chemical oxygen demand (COD), and heavy metals, were effectively removed. The pH was observed to be maintained at 7–8 due to the alkalinity supplied by the sulfur–calcium carbonate (SC) pellet. The denitrification efficiency and start-up period were observed to be affected by the influent quality. Chromium, iron, nickel, copper, and zinc—the major heavy metal components of the influent—were effectively reduced at certain concentrations. Other metal ions were also detected and reduced to undetectable concentrations, but no trends in the comparison with denitrification were observed. From the results it can be concluded that SOD is effective for the removal of nitrogen, particularly nitrates, without a drastic pH change, and can effectively remove minute concentrations of heavy metals and COD in metal plating wastewaters.

硫化水素を用いたＣｕ，Ｚｎ，Ｎｉ混合めっき廃水の選択的硫化による金属硫化物の分離

Experiments were conducted to investigate selective sulfuration of copper, zinc and nickel contained in a simulated plating wastewater using H2S as a sulfurating agent. The sulfuration of single solutions of copper, zinc and nickel, and mixed solutions of these metals with H2S was conducted in a bubble column reactor.As a result, it was found that heavy metals can be selectively precipitated from the mixed-metal plating wastewater at a pH value of 1.5 for copper, 4.5 for zinc and 6.7±0.2 for nickel. The purities of precipitates based on total amount of metal contained were 95.5%, 87.4% and 94.7% in the case of copper, zinc and nickel, respectively. When the results were compared with those obtained for the selective precipitation with Na2S, it was found that higher purities of metal sulfides were achieved with H2S. It was considered that local increases of pH resulting from an addition of alkaline sulfurating agent of Na2S were avoided in the case of H2S. Consequently, an undesirable co-precipitation of zinc and nickel sulfides at a pH value of 1.5 corresponding to copper selective precipitation was reduced. Similarly, the precipitation of nickel sulfide was partially avoided during the precipitation of zinc sulfide at a pH value of 4.5.

Characterization of primary precipitate composition formed during co-removal of Cr(VI) with Cu(II) in synthetic wastewater

Hexavalent chromium [Cr(VI)] cannot react with either carbonate or hydroxide to form chromium precipitates. However, by using a precipitation technology to treat plating wastewater containing Cr(VI), Cu(II), Ni(II) and Zn(II), approximately 78% of Cr(VI) (initial 60 mg/L) was co-removed with the precipitation of Cu(II), Ni(II) and Zn(II) (each 150 mg/L) by dosing with Na2CO3 (Sun 2003). Direct precipitation by forming Cu(II)-Cr(VI) precipitates followed by adsorption of Cr(VI) onto freshly formed Cu-precipitates was subsequently found to be the main mechanism(s) involved in Cr(VI) co-removal with Cu(II) precipitation by dosing Na2CO3 stepwise to various pH values (Sun et al. 2003). This study was. carried out to further characterize the formation of primary precipitates during the early stages of copper precipitation and simultaneous removal of Cr(VI) with Cu(II). Test metal-solutions were prepared with industrial grade chemicals: CuCl2 x 2H2O, Na2SO4 and K2Cr2207. NaCO3 was added drop-wise to synthetic metal-solution to progressively increase pH. For each pH increment, removal of soluble metals was detected by atomic absorption spectrophotometer (AAS) and surface morphology of precipitates was analyzed by scanning electron microscope (SEM). To further characterize the formation of primary precipitates, a series of MINEQL+ thermodynamic calculations/analyses and equilibrium calculations/ analyses were conducted. MINEQL+ thermodynamic calculation indicated that, for a system containing 150 mg/L Cu(II) and 60 mg/L Cr(VI) with gradual Na2CO3 dosing, if any precipitates can be formed at pH 5.0 or lower, it should be in the form of CuCrO4. Comparison tests using systems containing the same equivalent of Cu(II) plus Cr(VI) and Cu(II) plus SO4(2-) showed that the precipitation occurred at a pH of around 5.0 in the Cu(II)-Cr(VI) system and around 6.0 in the Cu(II)-SO4(2-) system. The discrepancy of the precipitation was indeed caused by the formation of Cu-Cr precipitates. The initiation of copper removal at pH around 5.0 for the Cu-Cr co-removal test was not attributable to the formation of Cu-CO3 precipitates, instead, it was most likely through the formation of insoluble Cu-Cr precipitates, such as CuCrO4 and CuCrO4 x 2Cu(OH)2. Experimental tests, equilibrium calculations, MINEQL+ thermodynamic calculations and surface morphologies for systems using higher concentrations of Cu(II) and Cr(VI) further verified the most probable composition of primary precipitates is copper-chromate. In the Cu-Cr co-removal test with Na2O3 dosing to increase pH and induce metal precipitation, copper-chromate precipitates are the primary precipitates produced and contribute to the initial simultaneous removal of copper and chromium.

Development of an ion exchange system for plating wastewater treatment

Ion exchange technology was applied to this study to treat nickel ion from plating wastewater which contains heavy metal, bringing environmental problems such as chromium, zinc, copper, and lead. To separate nickel ion from wastewater, the nickel recovery unit (NRU) used a column packed with strongly acidic cation resin. The leak of the ion appeared when rinse water that has a concentration of 1.8 g-Ni/L-distilled water flowed into the NRU as much as 20 times the bed volume. At this time, the capacity of resin packed in the column was 1.7 meq/ml and over 99% nickel ion was removed. Sulfuric acid was employed with a reagent in order to regenerate nickel ion from the resin adsorbed. Nickel ion recovered by sulfuric acid was obtainable up to 120 g-Ni/L. The concentration of sulfuric acid was 2N and space velocity was 2/h. Acid retardation unit (ARU) experiment could be accomplished by deacidification to control the pH of the solution to recycle in the plating process. The composition was 30 g-Ni/L and the pH maintained was over 3.0.

Studies on recovery of hexavalent chromium from plating wastewater by supported liquid membrane using tri- n-butyl phosphate as carrier

The transport of chromium(VI) ions from an aqueous feed solution through a flat type supported liquid membrane (SLM) containing tri- n-butyl phosphate (TBP) as carrier was studied. The influence of pH on the source phase, effect of concentration of receiving phase, stirring speed, effect of initial Cr(VI) concentration, feed to strip ratio and the influence of support characteristics was studied. Polytetrafluoroethylene (PTFE) with 1.0 μm pore size was found to have more flux permeability than 0.50 μm. The results indicated that the aqueous feed solution at pH 1 ± 0.1 to have high permeability. The initial feed phase Cr(VI) concentration of 9.6 × 10 − 4 M can be completely extracted and stripped with 0.50 M sodium hydroxide as stripping solution within 8 h. Stirring of aqueous solutions at 500 rpm with a magnetic stirrer showed high transport rate. After ten transport studies with one impregnation of carrier, the TBP carrier showed no significant loss in its permeability and retained the same transport ability. Under the optimum conditions chromium(VI) recovery from real plating wastewater was tested and found to be satisfactory with a flux value of 1.4 × 10 − 3 mol/m 2/s.

Recycling of Wastewater Containing Iron-Complex Cyanides Using UV Photodecomposition and UV Ozone Oxidation in Combination with an Ion-Exchange Resin Method

Wastewater contaminated with iron-complex cyanides was processed by UV photodecomposition accompanied by an iron elimination process using an iron-adsorbent. The wastewater processed by UV photodecomposition was oxidized by ozone combined with UV irradiation. The treated water was deionized by an ion-exchange resin method. This combined processes further increased the production of the pure water volume compared to a single process using an ion-exchange resin. The technique developed in this study can be summarized as follows. First, the iron-complex cyanides in plating wastewater were converted into aquapentacyanoferrate(III) [Fe(CN) 5 (H 2 O)] 3 - ion. Following the application of UV irradiation, it was decomposed into iron and cyanide (CN - ) ion. The iron was removed from the water in the form of Fe(OH) 3 by processing the wastewater with ozone and an iron-adsorbent. The CN - ion was oxidized to the cyanate (OCN - ) form by UV ozone oxidation in a relatively short time. The processed water was de-ionized by passing through cation and anion-exchange resins. The deionized water could be reused as rinsing water in a plating process. The results reported here suggest that wastewater contaminated with chemically stable iron-complex cyanides can be effectively recycled.

めっき廃液中の銅，亜鉛およびニッケルの硫化反応による選択的分離回収

Selective recovery of copper, zinc and nickel from electroplating wastewater was studied by precipitating the metal sulfides formed by sulfuration treatment. CuSO4, ZnSO4 and NiSO4 involved in model solutions and those of plating wastewater were adjusted to 100-120mg dm−3 of the initial metal concentration. Two kinds of sulfurating agents, sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) of 6.8×10−2 mol dm−3, were employed.As a result, it was found that Na2S was more effective for the separation of the metal sulfides precipitated. The formation of metal sulfides was dependent on the pH value of the solution. In the sulfuration process using Na2S, copper was first separated from the solution as copper sulfide in pH1.4-1.5, followed by the formation of zinc sulfide in pH2.4-2.5. Subsequently, nickel sulfide was precipitated after the formation of copper and zinc sulfides in the residual solution in pH5.5-6.0.The same results of the formation behavior of copper sulfide, zinc sulfide and nickel sulfide in a simulated plating solution were obtained for those in an electroplating solution.

Electrochemical treatment of heavy metals (Cu2+, Cr6+, Ni2+) from industrial effluent and modeling of copper reduction

An electrochemical technique was tested in a laboratory scale to treat heavy metals (Cu2+, Cr6+ and Ni2+) from plating industrial effluent. The experiments were performed in a membrane reactor having a capacity of 1 l. Stainless-steel sheets with surface area of 0.011 m2 and titanium coated with ruthenium oxide were used as cathode and anode, respectively. The electrolyte was circulated at a constant flow rate (0.42 l/min) and the pH was kept constant at 1. Applied current densities were 10 and 90 A/m2. According to the experiment, it was found that a membrane reactor with plane electrode was capable for treating plating wastewater with low energy consumption (42.30 kWh/kg metal) and low operating cost (5.43 US dollars/m3). More than 99% of metal reduction was achieved and the final concentrations of copper, chromium and nickel in treated water were 0.10-0.13, 0.19-0.20 and 0.05-0.13 ppm, respectively. The brightener had no effect on copper reduction whereas hexavalent chromium had strong effect. The kinetic of copper reduction in the presence of hexavalent chromium was modeled as a two-step process with respect to copper concentration.

Process analysis for treatment of industrial plating wastewater: simulation and control approach

One of the better options to remove chromium VI (Cr(VI)) from wastewaters is the electrochemical continuous reactor. This process can be used to clean rinse waters from the plating industry. A mathematical model of the reactor is developed by classical application of mass balances for Cr(VI) and Fe, both corroborated in a bench scale electrochemical reactor. The reactor model is employed as the real process where the proposed controller is implemented. For the controller synthesis a reduced order uncertainty estimator is employed to infer the reaction rate, which is assumed unknown and an input/output linearising controller is designed, using the input flow to the reactor as control input and the Cr(VI) concentration in the wastewater as controlled variable. This procedure yields a nonlinear PI controller; where new tuning rules are given. Stability analysis of the closed loop behaviour of the reactor under the proposed methodology is done via mathematical analysis of the equations that describe the dynamic behaviour of the estimation and regulation errors. The performance of the controlled reactor is illustrated with numerical simulations.

メッキ廃液からの有価金属の回収に関する研究 Ｉ 化合物沈澱法によるＮｉの回収

Since Ni is a valuable resources and its plating solution is costly, improvements in recycling technique from waste solution and slurry in the Ni plating process have been an necessity. In this paper, the retrieval of Ni from the electroless plating waste waters, especially worn-out ones with high concentration of Ni is considered. The compound precipitation method which retrieves Ni from waste waters as carbonate form or oxalate form is examined.The results show that higher solution temperature is preferable, and that Fe can be removed by neutralization precipitation. Among carbonate, Na2CO3 turns out to be the more effective precipitator than NaHCO3. When the double dose or more of the theoretical equivalent of Na2CO3 were added, and the initial pH was larger than 2, precipitation took the form of weak crystalline whose composition was Ni(CO)3(OH)4 · 4H2O. When NaHCO3 was used as precipitator, together with CO2 bubbling, globular particles precipitated.For oxalate, crystalline particles of NiC2O4 · 2H2O precipitated. The method was tested for waste water from an actual plant and followings were suggested: Ni-B solution should be precipitated with carbonate, while Ni-P solution with oxalates.

Empleo de microalga <i>Scenedesmus obliquas</i> en la eliminación de cromo presente en aguas residuales galvánicas

Dumping wastewaters from plating industry with a high content in chromium is a potential hazard for people and environment. It is known that some metals, including the heavy metals, at low concentrations participate in different metabolic routes, but at high concentration are toxic for many living organisms. Some microorganism taking the heavy metals from the environment are capable of concentrating and accumulating large quantities of them in different citoplasmatic structures with no-toxic effects. Microalgae have affinity by the polyvalent metals making possible their use as depollutant agent in waters that contains dissolved metallic ions as alternative methods when others methods of recycle are unusable. In this report a chromium removal study from a plating wastewater, using scenedesmus obliquus culture was made. The removal efficiency of Cr (VI) was 12 % and Cr (III) was 27 % and for condition of algae's immobilization removal of Cr (III) was 95 %.

Nickel removal from nickel plating waste water using a biologically active moving-bed sand filter.

Efficient removal of dissolved nickel was observed in a biologically active moving-bed 'MERESAFIN' sand filter treating rinsing water from an electroless nickel plating plant. Although nickel is fully soluble in this waste water, its passage through the sand filter promoted rapid removal of approximately 1 mg Ni/l. The speciation of Ni in the waste water was modelled; the most probable precipitates forming under the conditions in the filter were predicted using PHREEQC. Analyses of the Ni-containing biosludge using chemical, electron microscopical and X-ray spectroscopic techniques confirmed crystallisation of nickel phosphate as arupite (Ni3(PO4)2 x 8H2O), together with hydroxyapatite within the bacterial biofilm on the filter sand grains. Biosorption contributed less than 1% of the overall sequestered nickel. Metabolising bacteria are essential for the process; the definitive role of specific components of the mixed population is undefined but the increase in pH promoted by metabolic activity of some microbial components is likely to promote nickel desolubilisation by others.

Photocatalytic ZnO nanopowders prepared by solution combustion method for noble metal recovery

Nano-sized ZnO powder was synthesized by solution combustion method (SCM). Using this ZnO nanopowder as a photocatalyst, it was tried to recover silver from the silver-plating wastewater that was discharged by noble metal plating industries. The photocatalytic efficiency of ZnO nanopowder, as one of optical properties, was compared with other photocatalysts such as commercial TiO2 and commercial ZnO. The ZnO nanopowder showed three folds higher photocatalytic efficiency than any other commercial photocatalysts. Other electro-optical measurements such as photoluminescence (PL) measurement, electrical resistivity and carrier concentration measurement also showed very consistent results. The recovery of gold from gold plating wastewater was also tried. The recovery efficiency was improved by about 25% by adding methanol as a scavenger to the gold plating wastewater. It took 45 min to completely recover gold from the wastewater.