TWI396664B - A method for precipitating metal oxides from an aqueous waste solution - Google Patents

Description

Method for precipitating metal oxide from sewage solution

The present invention relates to a method of treating a wastewater stream comprising a metal oxide, and more particularly to a method of treating a wastewater stream to recover reusable reactants and possible metals (e.g., copper, tin, lead, and iron) from a solution, The primary application is to treat spent tin or tin/lead stripping solutions used in the electronics industry, particularly in the manufacture of printed circuit boards.

Background of the invention

With the development of applications and markets for different electronic devices, printed circuit board (PCB) manufacturing is growing rapidly. At this point, the average PCB manufacturing plant produces tons of effluent containing heavy metals. This hazardous waste is usually transported elsewhere for processing, which does not actually recycle the components and only reduces the volume of the waste prior to burial.

The nature of tin or tin/lead stripping solution

The most popular method of processing outer printed circuit boards (PCBs) in the United States and Europe is by pattern plating. In this common PCB fabrication method, tin or tin/lead is typically plated on the copper layer as an etch-resistant layer. After the non-circuit area of the copper layer is etched away, the next step is to strip the plated tin or tin/lead layer with a nitric acid-based solution to expose the copper circuitry.

The fresh stripping solution based on nitric acid contains nitric acid and ferric nitrate. Typical compositions are (weight/weight percent) 10-40% nitric acid, 1-10% ferric ion (Fe3 ⁺ ), <1 to 2% rust inhibitor and <1 to 3% suspending agent. Depending on the method of tin or tin/lead stripping modulus used, it is necessary to use a free nitric acid concentration of less than 3.6-4.2 N during stripping or a tin concentration of more than 50-100 g/l. Fresh stripping solution replaces the waste solution.

Normally, the waste stripping solution contains about 5-30% (w/w) nitric acid, 1-10% (w/w) iron ions (Fe ^{3 +} or Fe ^{2 +} ), and a small amount, <1 to 2% ( Weight/weight) rust inhibitor and <1 to 2.5% suspension, 2-20 g/L copper ion (Cu2 ⁺ ), about 10-200 g/L Sn ^{4 +} , and in some conditions about 0-5 g / l Pb ^{4 +} . If the oxidation is not complete, a small amount of Sn ^{2 +} or Pb ^{2 +} and other minor components may be present.

During the stripping reaction, the tin is oxidized to Sn ^{4 +} , which forms a tin oxide or hydroxide. Therefore, tin is mainly present in the wastewater stream as SnO ₂ . It is generally known that most tin salts are insoluble in water or even insoluble in any concentration of nitric acid. As the loading of the stripping solution increases, the metal tends to precipitate out of solution as a sludge. In spray applications, sludge can cause blockages in the nozzle. Suspending agents are used to prevent this blockage. The suspending agent retains the tin oxide in the solution by producing a fine dispersion of tin oxide in the stripper solution. These suspending agents are typically organic or inorganic acids such as those described by Kawanabe et al. in their patent "Strip solution for tin or tin alloys" (U.S. Patent No. 4,374,744).

When a certain metal loading content is reached, the stripping solution often becomes unstable, causing the possibility of an exothermic state, which is an immediate release of a large amount of heat. Typically the release of a large number of toxic NO _x gases during the heat-radiation state, and the stripping solution is excessively foamed. This state is a safety hazard in the factory and is the least popular. Obviously, the occurrence of an exothermic state can damage the operating equipment. The other ingredients in the fresh stripping solution (here referred to as rust inhibitors or nitric acid stabilizers) are used to solve this problem. These are often sulfur-free organic compounds containing nitrogen atoms as reported in U.S. Patent Nos. 4,374,744, 5,911,907, 5,512,201 and 5,244,539. In addition to their use as nitric acid stabilizers, these organic additives interact with metal oxides and salts or form complexes which result in altered and very complex chemical compositions.

Treatment of scrap tin or tin/lead stripping solution

A conventional method for treating a waste stripping solution is neutralization, for example by adding sodium hydroxide to neutralize free nitric acid. When the acid-base pH is adjusted to 8-13, most of the metal cations are converted to metal oxide or hydroxide precipitates. They can be further processed to recover metal tin, iron, copper or lead after filtration. The resulting filtrate is then evaporated to produce sodium nitrate crystals. Although the metals can be recovered satisfactorily, the possibility of recovery of the solution is lost. This method requires the use of a large amount of sodium hydroxide, and the resulting sodium nitrate crystals are not of commercial value.

An example of neutralization, the heading "A method for recovering metallic tin from a waste tin stripping solution", is disclosed in Taiwan Patent Publication No. 177,911, which uses a neutralizing agent, a precipitating agent and a reducing agent to make the treated effluent meet environmental requirements. And recovering metal tin from the waste stripping solution. When the method requires the use of a large amount of neutralizing agent and reducing agent, it undoubtedly has economic disadvantages.

Another method is described in the abstract of Taiwan Patent Publication No. 258,758, entitled "A Method and Apparatus for Regenerating a Tin-Plating Solution", which describes the separation of Fe, Cr and Sn ions from a plating solution by using an ion exchange resin to regenerate tin. Flux and a method of recovering metal tin. However, the methods stated by these inventors include complex steps which are not conducive to the treatment of spent tin/lead stripping solutions.

Another summary of the Taiwan Patent Publication No. 553,906, entitled "A Method for Treating Waste Tin-Lead Stripping Solution", teaches a multi-step process in which the tin and lead components of the waste stripping solution are first oxidized, the precipitate is removed and dissolved in the base. Or neutralize with strong acid and then reduce it electrolytically. This method is complex and requires many steps and several unit programs. In addition, additional chemicals must be introduced during various steps leading to increased costs and weaker profitability.

Among all these methods, the main emphasis is on the recovery of metals.

Accordingly, there is a need for a process for treating spent tin and tin/lead stripping solutions and recovering metal oxides in a manner that is environmentally tolerable, simple and efficient, cost effective, and in particular, that maintains the liquid phase active ingredients recyclable.

Summary of invention

It is an object of the present invention to provide a method of treating spent tin or tin/lead stripping solutions to recover valuable chemicals for reuse. More specifically, the desired recovery component is an aqueous reactive acid which may comprise other agents which are acceptable in fresh solutions. This is achieved by converting the organic compound present in the spent liquor by heat treatment, which also leads to the precipitation of heavy metal oxides. The remaining aqueous phase contains nitric acid, Fe and Cu ions, as well as negligible amount of Sn or Pb and is therefore suitable for reuse with or without further processing.

Another object of the invention is to treat spent tin or tin/lead stripping solutions to recover reusable nitric acid from the spent liquor.

Another object of the invention is to treat spent tin or tin/lead stripping solutions to recover metals from the spent liquor, such as copper, tin, lead or iron.

Another object of the invention is that the solution obtained after heat treatment according to the method can be recycled to a tin or tin/lead stripping process.

Another object is still to substantially reduce the volume of hazardous waste formation during PCB-manufacturing and thus reduce environmental load.

A significant benefit is also that there is no need to add chemicals that are different from existing chemicals during the process.

The present invention is based on stripping from tin or tin/lead by treating the aqueous solution at a temperature to initiate conversion of the organic additive to one or more of its precipitated derivatives and simultaneously precipitating the metal oxide (etc.). The solution precipitates and recovers valuable metal oxides.

Detailed description of the invention

This specification describes a method for precipitating metal oxides (etc.) from spent tin or tin/lead stripping solutions that still contain inorganic acids (etc.), metal salts and/or complexes, and one or more organic additives (etc.). And comprising treating the aqueous solution at a temperature and for a period of time to produce a conversion of the organic additive to its precipitated derivative and simultaneously precipitation of the metal oxide (etc.).

Organic additives, the key to their conversion to the clarity of waste solutions, contain organic amines. The organic amine remains in the aqueous solution in the form of a salt thereof (preferably a halide and more preferably a chloride thereof). The aqueous solution is treated at a temperature or, if desired, by the addition of a volume of about 100% nitric acid, which is initially converted to a compound that is less soluble under the reaction conditions and thus precipitates. Simultaneously, the metal oxide, which preferably comprises tin and/or lead oxide, also precipitates to produce the desired effect.

The amount of the organic amine is 0.2 to 5% (weight/weight), preferably 0.5 to 2% (weight/weight) and preferably 0.5 to 1% (weight/weight) based on the total weight of the waste tin or tin/lead stripping solution. The scope of). The amount of halogen (preferably in the form of its hydrohalide) is in the range of 0.2 to 2.0% by volume, preferably 0.5 to 1.0% by volume per volume of the total waste solution. The amount of metal oxide is in the range of from 1 to 300 g/liter, preferably from 10 to 120 g/liter and most preferably from 50 to 120 g/liter, in comparison with the total volume of the spent tin or tin/lead stripping solution. The conditions for producing the desired reaction include a high temperature in the range of from 55 to 210 ° C, preferably in the range of from 60 to 150 ° C and most preferably in the range of from 60 to 80 ° C.

If an optional step of enhancing the conversion of the organic additive to its precipitated derivative by the addition of nitric acid occurs, the amount of 100% nitric acid is 2-20% (vol/vol), preferably 5-10% (vol/vol) And the best 4.5-5.5% (vol/vol). Another method of initiating the reaction is to increase the pressure during the processing of the closed system. When nitric acid is added, the reaction temperature ranges from 68 ° C to 100 ° C, preferably from 70 ° C to 90 ° C and most preferably from 70 ° C to 85 ° C.

Another option to enhance the process for producing the conversion of the organic additive to its precipitated derivative is to effect the treatment under pressure. When the pressure is increased, it is in the range of from 1 to 16 bars during the processing of the closed system. The temperature is then in the range between 70 and 210 ° C, preferably from 100 ° C to 160 ° C.

The term "closed system" as used herein refers to a reactor in which the exchange of matter and energy with its environment is controlled. The inventors here use the autoclave from which the gas formed during the reaction cannot escape the system when needed, and as a result the pressure is simultaneously increased as the temperature rises. However, experiments conducted at temperatures below 100 ° C can also be performed in open systems.

In a preferred embodiment, the wastewater solution is a spent tin or tin/lead stripping solution. The method can further comprise recycling the recovered liquid phase back to the tin or tin/lead stripping process. If necessary, the copper content in the liquid phase or the liquid phase can be further reduced by extraction, ion exchange, chemical reduction reaction, eutectic crystallization or electrowinning to recover nitric acid, copper compound or iron compound. . Preferably, the solid phase comprises more than 80% of the total amount of tin in the spent tin or tin/lead stripping solution and the volume of the tin-containing portion is reduced to less than a quarter of the original volume.

The period required for the reaction to be reacted is from 1 to 30 hours, preferably from 50 minutes to 4 hours.

Under these conditions, the spent stream suspension becomes transparent at elevated temperatures and optionally at elevated pressures. The composition, which remains in solution under stripping conditions, separates into a solid phase and an aqueous phase. The phenomenon during autoclaving treatment involves the conversion of organic amines, their precipitation, the release of stannous oxide from the solution and the sedimentation of these precipitates. The temperature and pressure can be gradually increased. After cooling the mixture, the two phases can be readily separated by decantation, filtration, centrifugation or using any conventional technique. The solid phase has a high heavy metal content. In an experiment described in detail below, the solid phase comprised 70% SnO ₂ , which corresponds to a tin content of 54.8%.

The term "gradually increasing" means that the spent solution begins to react at the temperature in the shutdown system and then carries energy from the outside to heat the solution. The pressure increases with the temperature simultaneously.

An additional step is to recover the stripping chemicals for reuse. As stated, the primary objective is to recycle the recovered liquid phase back to the tin or tin/lead stripping process. Optionally, the liquid phase can be further processed to recover nitric acid, copper compounds or iron compounds. Those skilled in the art will be able to find many methods for these separations. For example, the copper content in the liquid phase can be reduced, for example, but not limited to, by extraction, ion exchange, chemical reduction, eutectic crystallization, electrowinning, or a combination of any of these methods.

As used herein, "waste tin or tin/lead stripping solution still contains inorganic acids (etc.), metal salts and/or complexes, and one or more organic additives (etc.)" refers to the complex pair to be treated. Side flux. It can be, for example but not limited to, from the chemical industry, metallurgy or the electronics industry. An example from the electronics industry is a waste tin or tin/lead stripping solution comprising nitric acid, iron, copper, tin and/or lead oxides and salts and an organic stabilizer for nitric acid. For accuracy, the term solution is commonly used for tin or tin/lead stripping solutions, although SnO _{2 is} actually dispersed in the liquid phase. This term is used herein when the term is used broadly in the art.

The inorganic acid used herein refers to a mineral acid present in a waste solution. In the case of a spent tin or tin/lead stripping solution the primary acid is nitric acid and the other will be a suspending agent that remains in the aqueous phase to prevent precipitation of the metal oxide. Typically the suspending agent is a mineral acid such as hydrochloric acid, nitric acid, sulfuric acid, fluoroboric acid, boric acid or chloric acid.

The Kawanabe patent (U.S. Patent No. 4,374,744) also teaches that organic acids can be used for this purpose. Examples of these are oxalic acid, acetic acid, propionic acid, gluconic acid, tartaric acid or formic acid. The organic addition compounds herein include these and nitric acid stabilizers as described below.

Here, the nitric acid stabilizer uses the meaning taught by Campbell in US 5,911,907. These are referred to as "rust inhibitors" when reporting the composition of fresh or spent tin or tin/lead stripping solutions. These compounds are added to suppress serious problems such as the cost of HNO ₃ and the generation of exothermic conditions during the treatment. Exotherm comprising tin and copper ions in the presence of toxic NO _x discharged from the nitric acid gas, and excessive etching of copper. The stabilizer concentration should be in the range of about 5-30 grams per liter. As a general indication, Campbell proposes "organic additives containing nitrogen but no sulfur". More specifically, the stabilizer is an organic amine, preferably a ring. Suitable nitric acid stabilizers include amino-triazole (preferably 4-amino-1,2,4-triazole) and amino-isoxazole (preferably 3-amino-5-methyliso) Oxazole). Other stabilizers provided by the patent documents are (U.S. Patents 4,374,744, 5,512,201 and 5,911,907) 4-amino-1,2,4-triazole, 1,1,1",1" hydroxyethylenediamine, 1, 2,3-triazole, 1,4-diazabicyclo[2.2.2]octane, 2,4-diamino-6-hydroxypyrimidine, 3,5-diamino-1,2,4- Triazole, 3-amino-5-methylisoxazole, 4-amino-antipyrine, 5-amino-3-methylisoxazole, alanine, benzotriazine Oxazole, cyclohexylamine, diethanolamine, diethyltriamine, ethylenediamine, glycine, hexamethylenetetramine, imidazole, oxazole, indole, thioglycolic acid, monoethanolamine, naphthoquinone Azole, N-ethyl-substituted imidazole, N-methyl-substituted imidazole, propanolamine, propylenediamine, pyrazole hydrochloride, pyrazole, pyrazolecarboxylic acid, pyrrole, pyrrolecarboxylic acid, three Oxalate hydrochloride, triazole, triethanolamine, tri-ethylpentamine, and 4-urocanic acid. Other additives containing sulfur and nitrogen, such as 2-aminobenzenesulfonamide, 3-aminesulfonyl-1-alanine, 4-(aminomethyl)benzenesulfonamide, 4-amino-6-chloro -1,3-phenyldisulfonamide, 4-carboxybenzenesulfonamide, aminomethanesulfonic acid, ammonium aminesulfonate, N-(2-thiazolyl)amine sulfonamide, sulfamethazine , sulfamide, methotrexate, amine sulfonamide, sulfisomidine, thioisoxazole and sulfadiazine.

"Conversion" of an organic compound implies any reaction that takes place in the organic component present in the spent solution, which occurs upon heating and as a result the solubility changes. These reactions include polymerization, degradation, oxidation, salt formation or typical reactions of other compounds. Depending on the solubility of the reaction product (etc.), the reaction product (etc.) may remain in solution or be transferred from the liquid phase to the precipitate. The sedimentation of the precipitate herein indicates how the above organic precipitate and SnO _{2 are} released by the treatment of the present invention to maintain their dispersing or dissolving properties, and they all sink to the bottom of the reactor.

Objects and advantages of the present invention will be described in more detail by way of non-limiting example and with reference to the drawings.

Instance

Two sets of examples were carried out, the first group representing the experiment under normal pressure and the second group representing experiments conducted under pressure.

Example 1

The spent tin stripping agent was analyzed to include 4% Sn, 24.4% NO ₃ , 0.9% organic C, 0.4% Cu, and 1.6% Fe in these tests.

Effect of adding 5% by weight of 100% HNO ₃ at 60 and 85 ° C

5% by weight of 100% HNO _{3 was} added to the sample of this waste tin stripping agent and stirred in a 1-liter glass reactor at 1 bar pressure and 60 ° C for 1 hour. No transparent layer was observed in the sink test. When heating was continued at 60 ° C for more than 2 hours, the suspension settled during 1 day to yield 79% by volume of a transparent layer and 21% by volume of settled SnO ₂ .

5% by weight of 100% HNO _{3 was} added to this sample of the waste tin stripping agent and stirred in a 1-liter glass reactor at 1 bar pressure and 85 ° C for 1 hour. It was observed during the reaction some NO _x - gas. The SnO ₂ -suspension settled during the 1 day period in the sedimentation test to yield 88% by volume of the transparent layer and 12% by volume of the settled SnO ₂ .

Example 2. Effect of higher nitric acid addition at 80 ° C

Add a) 0, b) 10, c) 20 and d) 30% by weight of 100% HNO ₃ to the sample of the waste tin stripper and stir in a 1-liter glass reactor at a pressure of 1 bar and 80 ° C 1 hour. The corresponding transparent layer after 1 day in the sink test was a) 80% by volume, b) 80% by volume, c) 78% by volume, and d) 73.5% by volume. 10-30 wt% by the addition of 100% HNO ₃ become lighter color was observed and NO _x - gas.

Example 3. Effect of temperature 60-67 ° C and 75 ° C on the original waste tin stripping agent

A sample of the original spent tin stripper, without the addition of nitric acid, was stirred in a 1-liter glass reactor at 1 bar pressure and 60 ° C for 1 hour and at 67 ° C for an additional 1.5 hours. SnO ₂ remained in suspension during the sink test and did not settle.

A sample of the original spent tin stripper, without the addition of nitric acid, was stirred in a 1-liter glass reactor at 1 bar pressure and 75 ° C for 1 hour. The SnO ₂ -suspension settled during the 1-day period in the sedimentation test to yield 81% by volume of clear layer and 19% by volume of settled SnO ₂ .

Example 4. Temperature 20-50 ° C and addition of 2-20% HNO ₃ did not affect

When 2 or 5% by weight of 100% HNO _{3 was} added to the sample of the waste tin stripping agent and stirred in a 1-liter glass reactor at 1 bar pressure and 20 ° C for 1 hour, no sedimentation occurred in the sinking test. Sedimentation was not observed by adding 20% of 100% HNO ₃ in the sinking test and stirring at 1 bar pressure and 28 or 50 ° C for 1 hour in a 1-liter glass reactor.

The conclusion of the experiment with 1 bar pressure:

The reaction for the scrap tin stripping agent to cause the sinking of SnO ₂ starts at about 70 ° C and starts at about 60 ° C when 5% by weight of 100% HNO ₃ is added. Even when 20% HNO ₃ was added, no reaction was observed at 50 °C. Nitric acid was added to produce higher levels of NO _x in more during the reaction - gas. The nitrates ranged from 24.4% by weight of NO ₃ to 41.8 % by weight of NO ₃ in these tests.

The combined liquid samples from all tests showed increased nitrate content due to the addition of nitric acid, similar amounts of copper, iron and organic carbon and lower tin content compared to the original sample. Tin is in the form of SnO ₂ in both the original suspension and the precipitate of precipitation.

Example 5. Experiments were carried out under pressure;

These experiments were carried out in a Parr titanium autoclave model 4563 at a maximum volume of about 1000 ml. The reactor was fitted with a double 4-bladed impeller connected to the motor by a magnetic couple. The stirring rate was 300 rpm. In order to protect the walls of the autoclave, a glass lining is used. The pressure is measured with a pressure gauge. The autoclave was heated using an electronic hood. At the end of the experiment, the cooling coils surrounding the impeller are connected to cool the liquid. For temperature measurement, two k-type thermocouples were placed in the autoclave via special openings. Once the thermocouple is connected to the control device (heater), it controls the electronic cover. The setpoint temperature can be programmed on this control unit. The second thermocouple is connected to a reference portable digital read meter. After the reaction, the autoclave was stopped with water. The acidity and concentration of the final solution were measured after pouring the contents of the autoclave.

The autoclave was filled to approximately 70% (vol/vol). Prior to the reaction, the reactor was flushed with nitrogen to remove all gaseous oxygen remaining in the system.

A spent tin stripper solution (700 ml) was received from the PCB producer and placed in the reactor after the preparation. The composition of the solution is about 12-15% (w/w) nitric acid, 5% (w/w) iron ions, Fe ³⁺ or Fe ²⁺ , and a small amount, <1% (w/w) rust inhibitor ( Anti-tarnish), and <1% suspension, 2-15 g/L copper ion Cu ²⁺ and about 10-120 g/L Sn ⁴⁺ . The rust inhibitor used herein is benzotriazole.

The experiment was carried out in the above manner. The temperature was initially 20 ° C and gradually rose to 210 ° C over a 5 hour reaction time. At the same time, the ground pressure rose from 1 bar to 15.2 bar.

After autoclaving, the spent tin stripper solution was split into two portions: a clear solution and a precipitate that settled down the bottom of the autoclave. The metal derivatives are separated into primary tin (98%, results of ICP analysis) precipitation and less than 2% remain in solution, whereas copper and iron derivatives remain in solution.

The important finding, when the increase of the pressure of the system, can be ignored releasing NO _x gases. This is a significant advantage compared to previous techniques.

Claims (19)

A method for precipitating a metal oxide from a spent tin or tin/lead stripping solution that still contains a mineral acid, a metal salt and/or a complex, and one or more organic amines, which is included at a temperature of 55-210 ° C and The aqueous solution is treated for 1 to 30 hours to produce a conversion of the organic amine to its precipitated derivative and at the same time a precipitation of the metal oxide, the converted form is divided into a solid phase and a liquid phase, and is added by adding nitric acid. The organic amine is converted to a precipitated derivative. The method of claim 1, wherein the organic amine in the scrap tin or tin/lead stripping solution is in its salt form. The method of claim 1 or 2 wherein the anion of the organic amine salt is a halide in the spent tin or tin/lead stripping solution. According to the method of claim 3, wherein the halide is selected to be a chloride. The method of claim 1 or 2, wherein the organic amine is benzotriazole. The method according to claim 1 or 2, wherein the amount of the organic amine is in the range of 0.2 to 5% (weight/weight) based on the total weight of the waste tin or tin/lead stripping solution. The method of claim 4, wherein the amount of the halide is in the range of 0.2 to 2.0% (volume/volume) of the total volume of the spent tin or tin/lead stripping solution. The method of claim 7, wherein the halide is optionally in the form of a hydrogen halide. According to the method of claim 6, wherein the metal oxide The amount is in the range of 1 to 300 g/liter compared to the total volume of the scrap tin or tin/lead stripping solution. According to the method of claim 1, the range of 68-100 ° C at atmospheric pressure is preferred. According to the method of claim 1, wherein the treatment for producing the derivative of the organic additive into its precipitate is enhanced under pressure. The method of claim 1, wherein a pressure is further provided in the closed system during the treatment so that the pressure is increased and is in the range of 1-6 bar. The method according to claim 12, wherein from 70 to 210 ° C is preferred. According to the method of claim 1, wherein the amount of nitric acid added is 2-20% (vol/vol) of the total volume of the spent tin or tin/lead stripping solution. According to the method of claim 1, the method further comprises recycling the at least partially recovered liquid phase to a tin or tin/lead stripping process. According to the method of claim 1, it comprises an additional step of further treating the liquid phase to recover nitric acid, a copper compound or an iron compound. According to the method of claim 16, wherein the copper content in the liquid phase is reduced by extraction, ion exchange, chemical reduction, eutectic crystallization or electrowinning. The method of claim 1, wherein the solid phase comprises an initial total amount of more than 70% tin in the spent tin or tin/lead stripping solution. The method of claim 1, wherein the liquid phase comprises less than 2% of the initial total amount of tin in the spent tin or tin/lead stripping solution.