Crossflow microfiltration has attracted attention for use in separating heavy metal hydroxides from wastewater from metal finishing processes, and is slated to replace conventional coagulation-precipitation. We determined the specific cake resistance and compressibility of filtrated metal hydroxide suspensions in constant-pressure dead-end filtration. Crossflow microfiltration experiments were done at a constant pressure and filtrate flux was measured for different crossflow velocities, transmembrane pressures, and concentrations. Results showed that 1) little difference existed in filtration properties within the pH range (9-11) studied; 2) the initial stage of filtration process was described by a cake filtration model; 3) the mean filtrate flux with backwashing was estimated roughly from filtration results without backwashing; and 4) the mean flux of highly concentrated suspensions depended strongly on crossflow velocity and weakly on transmembrane pressure, i. e., the critical flux existed at a lower transmembrane pressure.
Water-soluble cleaning replaces CFC cleaning has a problem of the gain of waste water. We have developed a glycol ether/water cleaning technique that recycles the cleaning agent, omits rinsing, and maintains of high detergency. The process, using a cleaning agent consisting of 35% glycol ether and 65% water, begins with a uniform solution at 30°C, which separates into two layers as the solution is heated to 60°C. The upper layer, consisting of 90% glycol ether, completely dissolves oil. The solution is then cooled. At 30°C the solution resumes its uniform state, leaving the oil separate. Once the oil is removed, the cleaning agent can be used again. The recycle of a glycol ether cleaning agent utilizes the dissolution and the separation with water by temperature. It is thought that the solubility of a glycol ether can be arranged with hydrophilic-lipophilic-balance (HLB) like a surfactant.
To recycle waste rinse water from metal surface finishing, the discharge is desalinated with a reverse osmosis(RO) membrane after filtration and its pH is adjusted to an acidic state. The fouling index(FI) had a reading of 4 in the acid(pH5) liquid after micro filtration by a 1μm cartridge filter element. The flow speed for the concentrated fluid was maintained at more than 0.1m/s to prevent precipitation of a suspended solid or adherence of an insoluble material to the membrane. This pretreatment allowed effective and stable desalination process for the waste rinse water using the RO membrane. The desalinated water was passed through a cation exchange resin column and an anion exchange resin column in a series. Water deionized by the ion exchange method after its desalinization using a RO membrane can be reused in the final rinsing process. The electric conductivity of permeated water from the RO membrane did not exceed 4.5mS/m and effluent from the anion exchange column was nearly 1mS/m. Based on these results, this process is a practical recycling system for discharge from surface finishing.
We studied the mechanism and conditions for Sn-Cu alloy electrodeposition using eutectic lead free solder (Sn: 99.3w%, Cu: 0.7w%). Polyoxyethylenelaurylether (POELE) was an important additive, producing a smooth surface with uniform component distribution. The melting point of the alloy was 227°C, satisfying the eutectic temperature requirement for lead-free solders. We found that POELE adsorbs selectively on the deposited Sn surface, then suppresses subsequent deposition of both Sn and Cu during electrolysis.
Dross discharged from practical operations was immersed in a molten lead bath between 703K and 823K to study zinc separarion >from dross on a laboratory scale. Dross was composed mostly of zinc and intermetallic compounds of zinc and iron. Solidified dross and a lead bath were analyzed by X-ray diffraction (XRD) and fluorescent X-ray analysis. The zinc in dross decreased gradually with treatment time, while that of lead increased. Zinc is supposedly separated from both the zinc and intermatallic phases when dross was treated in a lead bath. Zinc floated in lead due to its lighter specific gravity. The amount of zinc floating increased with treatment. Dross treated long time consisted of discrete iron and lead was magnetic. During immersion, lead penetrated dross and replaced zinc. Zinc and lead do not dissolve mutually from the view point of thermodynamics. Iron in dross neither formed compounds with lead nor dissolved in the lead phase. This process thus enabled zinc and iron to be separated from dross in a practical process.
We studied nitrate reduction with hydrogen in Cu-Pt black catalysts with various surface compositions. Nitrate removal is extremely slow in Pt and Cu catalysts alone, but enhanced in Pt black catalysts with Cu atoms. Hydrogen is oxidized at Pt sites, and nitrate reduced at Cu sites. We examined the relationship between nitrate concentration and reaction time and found that nitrate removal in Cu-Pt black catalysts is apparently a first-order reaction. Cu coverage affects selectivity of the products of the Cu-Pt black catalyst. The main product of nitrate reduction was nitrite in Pt black catalysts with Cu coverage of about 0.6, where nitrite would be reduced to nitrogen, though the reaction is slow. The maximum rate constant is 5.3×10-6m min-1 in Pt black catalysts with Cu coverage of about 0.85, where the main nitrate reduction products were ammonia and nitrogen.
Ionic migration often observed in the presence of moisture causes short circuits between electrodes on printed circuit boards and reduces reliability. Many reports suggest that anode dissolution rate and cathode deposition rate affect ionic migration time when short circuits occur. Therefore, to analyze these ionic migration processes, in situ measurement of anode and cathode surface reactions is indispensable. We have already reported that in situ measurement of silver, copper, or solder migration in de-ionited distilled water is possible by applying a quartz crystal microbalance (QCM). We report here the migration processes of lead-free solder in air and nitrogen atmospheres by means of QCM. We found that the main deposited component of lead-free solder is tin, that of older lead-based solders is lead, and that lead-free solder is less prone to migration than older lead-based solders.
We investigated the effect of polymer systems having carboxyl groups as corrosion inhibitors on the corrosion of mild steel in cooling water systems We found that a ternary copolymer composed of acrylic acid (AA), acrylamide (AAm) and acryloylmorpholine (AMo) was a good corrosion inhibitor Its maximum inhibition efficiency was more than 90%, and formation of scale was limited by an addition of the copolymer in a solution with high concentrations of ionic species For this copolymer system, in the relationship between molecular structure and corrosion inhibition capability, essential factors were that i) the number average molecular weight was about 7×103 to 1×104, ii) the content of AA was about 70mol%, iii) the bond-structure of carboxyl group to polymer main chain was a direct one, and iv) the functional groups except for the carboxyl group were AAm and AMo A ternary copolymer having these characteristics is potentially an effective inhibitor of corrosion of mild steel.
Corrosion rates of Cr-P-C alloy plating film produced using a trivalent chromium bath were measured in hydrochloric acid, hydrofluoric acid, aqua regia, sulfuric acid, nitric acid and sodium hydroxide solutions by a weighting method, and compared with those of conventional Cr plating film produced using a hexavalent chromium bath. And corrosion behavior of both films in a hydrochloric acid solution were studied using electrochemical polarization measurements and XPS analysis. Cr-P-C alloy plating film was found to have an extremely high corrosion resistance even in hydrochloric acid, hydrofluoric acid and an aqua regia solution, while the conventional chromium film dissolved completely in those solutions. XPS studies revealed that Cr-P-C alloy plating film was covered by a chromium oxide layer on top of the film surface. Metallic phosphorus concentrated under the oxide layer, which protects the alloy from corrosion in a hydrochloric acid solution.
Zinc oxide film was prepared easily by cathodic deposition from zinc nitrate aqueous solutions. Deposited film was evaluated as photocatalytic film under different deposition conditions. Photocatalysis was evaluated by measuring acetaldehyde gas degradation. Film prepared in dilute solutions of Zn (NO3)2 showed superior photocatalysis activity. Film prepared under high current density showed superior photocatalysis. We monitored mass changes during cathodic deposition and confirmed that ZnO was completely deposited under the above conditions and that additional reactions took place under other preparation conditions. These additional reaction deactivated photocatalysis.
All surface treatment waste water except concentrated waste solutions from pre-treatment, plating, and post-treatment has been separated into acid-alkaline, chromic, and cyanide waste water, mixed after chromium reduction and cyanide oxidation, and treated a process that generate large amounts of sludge. Components cannot be completely separated and recovered from such water even if methods like ion-exchange are used. Considering environmental protection and effective use of resources and energy, process components should be recovered, regenerated, and recycled for each process in non waste water treatment. Using electrodialysis (ED) under the proper conditions (electrode solution, voltage, flow rate, membrane distance, number of compartment, etc.), spent plating solutions are concentrated and desalted for recycling as plating solutions and water. ED treats plating solutions at room temperature and requires no energy except electric power, no chemicals for separating components, and no membrane regeneration making it applicable to plating recycling. We constructed ED installations and studied the recovery of metals and water from copper sulfamate/nickel sulfamate multilayer alloy plating baths. We effectively recovered copper, nickel and water with an ED installation having a membrane distance of 5mm and operated using 0.05M sulfamic acid as the electrode solution at 7.5V.