FI121569B - Process for precipitating metal oxides from a wastewater solution - Google Patents

Description

Method for precipitating metal oxides from sewage solution - Metallurgy - Metal oxide ur et avloppsvattenlösning

FIELD OF THE INVENTION

The present invention relates to a process for treating spent metal or oxide etching solutions of tin or tin lead. More particularly, the present invention relates to a process for treating waste water streams to recover reusable starting materials and possibly metals such as copper, tin, lead and iron from the solution. The etching solution of tin or tin lead is used in the electronics industry, especially in the manufacture of circuit boards.

BACKGROUND OF THE INVENTION

The production of printed circuit boards (PCBs) is growing rapidly with the increasing number of applications and markets for various types of electrical equipment. At present, a conventional PCB manufacturing plant produces tons of heavy metals containing wastewater. This hazardous waste is usually transported elsewhere for treatment, which does not actually recycle components but merely reduces the volume before burial.

Nature of the etching solution of tin or tin lead

The most popular method of surface treatment of printed circuit boards (PCBs) in the United States and Europe is pattern coating. In this conventional circuit board manufacturing method, a tin or tin lead layer is applied to the copper layer by an electrical coating o, which acts as an anti-corrosion layer. After the non-wiring areas of the copper layer have been removed by etching, the next step is to use a nitric acid-based solution electrically to remove the plated tin or tin lead layer to expose the copper wiring .x.

cc: - Q_ T- Fresh etching solutions based on nitric acid are nitric acid and ferric nitrate.

A typical composition is (by weight, w / w) 10-40% nitric acid,? 1-10% ferric ion Fe3 +, <1-2% anti-darkening agent and <1-3% suspending agent. When the free nitric acid content is less than 3.6-4.2 N or the tin content is greater than 50-100 g / l, depending on the process conditions of the tin or tin lead etching module 2 used, the spent solution must be replaced by a fresh etching solution.

Typically, the spent etching solution contains about 5-30% (w / w) nitric acid, 1-10% (w / w) ferric ion Fe 3+ or Fe 2+ and minor amounts, <1-2%, 5 (w / w) an anti-darkening agent and <1-2.5% suspending agent, 2-20 g / l Cu2 + copper ion, about 10-200 g / l Sn4 + and in some cases about 0-5 g / l Pb4 +. It may contain minor amounts of Sn2 + or Pb2 + ions if oxidation has been incomplete, and minor amounts of other components.

During the etching reaction, the tin is oxidized to the Sn4 + ion which forms tin oxides or hydroxides. Thus, tin is present in waste streams mainly as SnCl2. It is known that most tin (IV) salts are insoluble in water or even nitric acid, whatever its concentration. As the metal load increases in the etching solution, the metal tends to precipitate from the solution as a slurry. In spray applications, the slurry may cause clogging of the spray nozzles. To prevent this, a suspending agent is used. The suspending agent holds tin (IV) oxide in solution by forming a fine dispersion of tin (IV) oxides in the etching solution. Such suspending agents are typically organic or inorganic acids as described, for example, in U.S. Patent No. 4,374,744 to Kawanabe et al., Entitled "Stripping solution for tin oro alloys".

20 When a certain metal load is reached, the etching solution often becomes unstable, which may cause exothermic conditions, meaning that a large amount of heat is released rapidly. Typically, under exothermic conditions, large quantities of toxic NOx gases are released and the etching solution foams excessively. These conditions pose a safety risk at the factory and are highly undesirable. It is clear that the presence of exothermic conditions can damage the drive equipment. To solve this problem, a component added to a fresh etching solution, referred to herein as an anti-dark agent, is used.

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-1 or nitric acid stabilizer. These are often organic compounds that do not | containing sulfur but containing a nitrogen atom, and are disclosed, for example, in U.S. Patent Nos. 4,374,744, 5,911,907, 5,512,201, and 5,244,539. In addition to acting as nitric acid stabilizers, these organic additives are believed to be interact with or form complexes with metal oxides and salts, thereby producing variable and highly complex chemical compositions.

3 Treatment of spent tin or tin lead etching solution

One conventional method of treating a spent etching solution is neutralization, for example by adding sodium hydroxide to neutralize free nitric acid. When the pH is adjusted to a range of 8-13, most of the metal cations are converted to metal oxide or hydroxide precipitates. After filtration, they can be further processed to recover metallic tin, iron, copper or lead. The filtrate thus obtained is then evaporated to form sodium nitrate crystals. Although metals can be recovered satisfactorily, the possibility of recycling the solution is lost. The process requires the use of large amounts of sodium hydroxide 10 and the resulting sodium nitrate crystals have no commercial value.

As an example of neutralization, the use of a neutralizing agent, a precipitant and a reductant to bring the treated waste water to an environmentally compatible standard and to recover the metal tin from the recovery process is disclosed in the summary of Taiwan Patent Publication 177,911 entitled "A method for recovering metallic tin from spent tin stripping solutions". As the process of the above patent requires the use of large amounts of neutralizing agent and reducing agent, it certainly has economic disadvantages.

Another procedure is disclosed in the summary of Taiwan Patent Publication 258,758, entitled "A method and apparatus for the regeneration of a tin-20 electroplating solution" which describes a method for separating Fe, Cr and Sn ions from a solution used in electrodeposition using ion exchange resins in tin flux. for regeneration and metal tin recovery. However, the process disclosed by these inventors involves complex operations, so that the process is not advantageous for the treatment of the spent tin lead etching solution.

0 01 25 Another summary of Taiwanese Patent Publication 553,906, entitled "A method for treating waste tin-lead stripping solution", discloses a multi-step method in which the tin (IV) and lead (II) The compounds are first oxidized at 45-120 ° C, the precipitate is removed and dissolved in a base or a strong acid and then electrolytically reduced.This method is complicated and requires many steps and several unit processes. chemicals need to be added over the course of the year, which increases costs and reduces profitability.

In all these methods, the emphasis is on metal recovery.

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Therefore, there is a need for a process for treating spent tin and tin lead etching solutions and for recovering metal oxides in an environmentally friendly, simple and efficient manner, and in particular to retain the active ingredients in a liquid phase for recycling.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for treating wastewater streams for the recovery of valuable chemicals for reuse. More particularly, the desired recyclable component is an aqueous reactive acid solution which may contain other substances permitted in the fresh solution. This is achieved by converting the organic compound contained in the waste by heat treatment, which also results in the precipitation of heavy metal oxides. The remaining aqueous phase then contains nitric acid, Fe and Cu ions, but insignificant amounts of Sn or Pb and is thus suitable for recycling as such or after further treatment. More specifically, the process of the invention is defined in claim 1.

One embodiment of the invention is to treat spent etching solutions of tin or lead in order to recover the reusable nitric acid from the waste. Another embodiment of the invention is to treat spent tin or tin lead etching solutions to recover metals such as copper, tin, lead or iron from waste.

It is an object of the present invention that the solution obtained after the heat treatment according to the process can be recycled to the etching process of tin or tin lead.

A further aim is to significantly reduce the volume of hazardous waste generated during PCB manufacturing and thereby reduce the environmental load.

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It is also a significant advantage that no additional chemicals are added during the process in addition to those who were present.

The present invention is based on the surprising discovery that valuable metal oxides can be precipitated and recovered from the effluent solution by treating said aqueous solution at a temperature at which conversion of said organic additive to at least one of its precipitating derivatives and simultaneous precipitation of the -side (s) begins.

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DETAILED DESCRIPTION OF THE INVENTION

The present disclosure describes a process for precipitating metal oxide (s) from a waste water solution further comprising (at least one) inorganic acid, metal salt and / or complexes and at least one organic additive, wherein said aqueous solution is treated at such a temperature and temperature. for a period of time that provides conversion of said organic additive to a precipitating derivative and co-precipitation of said metal oxide (s).

The organic additive whose conversion is the key to purification of the waste solution comprises an organic amine, preferably benzotriazole. While remaining in the aqueous solution, the organic amine is in the form of its salt, preferably the halogen and more preferably the chloride salt. Treatment of said aqueous solution at a certain temperature, or optionally further enhancement by addition of a certain volume of about 100% nitric acid, initiates the conversion of said organic amine salt to a compound having a lower solubility under the reaction conditions and thus its precipitation. At the same time, said metal oxides, which preferably comprise tin (IV) and / or lead (II) oxides, precipitate to give the desired effect.

The organic amine is present in an amount of 0.2-5% (w / w), preferably 0.5-2% (w / w) and most preferably 0.5-1% (w / w) of the total weight of the waste water solution. The amount of halogen, preferably in the form of hydrogen halide, is from 0.2 to 2% (v / v), preferably from 0.5 to 1.0% (v / v) of the total waste solution. The amount of metal oxides is 1-300 g / l, preferably 10-120 g / l, and most preferably 50-120 g / l of the total volume of the effluent solution.

The conditions for achieving the desired reactions are an elevated temperature of 55 to 210 ° C, preferably 60 to 150 ° C, and most preferably 60 to 80 ° C. If an optional procedure is selected to enhance conversion of said organic additive to its precipitated derivative by addition of nitric acid, 2% to 20% (v / v), preferably 5% to 10% (v / v) of 100% nitric acid is added and

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most preferably 4.5 to 5.5% (v / v). Another way to effect the reaction initiator 30 is by increasing the pressure in the closed system during treatment, o

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§ In this context, "closed system" means a reactor whose material and energy exchange with the environment is controlled. If necessary, the inventors then used an autoclave, which prevents the gases formed during the reaction from escaping from the system, causing the pressure to rise while the temperature 6 rises. However, experiments below 100 ° C could also be performed in an open system.

According to a preferred embodiment, the effluent solution is a spent tin or tin lead etching solution. The method may further comprise recycling the recovered liquid phase 5 back to the tin or tin lead etching process. Optionally, the copper content of the liquid phase is reduced by extraction, ion exchange, chemical reduction, eutectic crystallization or electrolytic enrichment, or the liquid phase can be further treated to recover nitric acid, copper compounds or iron compounds. Preferably, the solid phase contains more than 80% of the initial total amount of tin in the effluent solution, and the volume of the tin-containing fraction is reduced to less than a quarter of the original volume.

The time required for the desired reactions is 1 to 30 hours, preferably 50 minutes to 4 hours.

Under these conditions, at elevated temperature and optionally elevated pressure, the waste stream suspension becomes clearer. The composition, which remains solution-like under the etching conditions, separates into a solid phase and an aqueous phase. Phenomena during autoclaving include the conversion of an organic amine, its precipitation, the release of tin (II) oxide as a precipitate from solution, and the deposition of these precipitates. The temperature and pressure can be increased gradually. After cooling the mixture, the two phases can be easily separated by decantation, filtration, centrifugation or any conventional technique. The heavy metal content of the solid phase is high. In one of the experiments described in detail below, the solid phase contained 70% SnC 2, corresponding to a tin content of 54.8%.

By "gradually increasing" it is meant that the reaction is initiated at a temperature of a solution of the waste solution in a closed system, after which energy is introduced from outside to warm the solution. The pressure increases with the temperature.

| The purpose of the additional steps is to recover the etching chemicals for reuse. As described above, the main purpose is to recycle the recovered liquid o 30 phase back into the etching process of tin or tin lead. Optionally, this liquid phase may be further treated to recover nitric acid,

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^ compounds of iron or iron. One skilled in the art will be able to come up with several ways to make these distinctions. For example, the copper content of the liquid phase may be reduced, for example, but not limited to, extraction, ion exchange, ceramic reduction, eutectic crystallization, electrolytic enrichment, or any combination thereof.

As used herein, '' wastewater solution further comprising (at least one) inorganic acid, metal salts and / or complexes, and at least one organic additive 'denotes a complex side stream to be treated. For example, it may be derived from, but not limited to, the chemical, metallurgical, or electronics industries. An example from the electronics industry is a spent tin or tin lead etching solution containing nitric acid, iron (II), copper (I), tin (IV) and / or lead (II) oxides and salts and organic stabilizer nitric acid. for. To be precise, the solution is usually used for a tin or tin lead etching solution, although in fact SnO2 is dispersed in the liquid phase. This term is used in this context because it is widely used in the art.

By inorganic acids is meant inorganic acids in this waste solution. In the case of the spent tin or tin lead etching solution, the main acid is nitric acid and the other would be suspending agents to prevent the precipitation of metal oxides and to keep them in the aqueous phase. Suspending agents are typically inorganic acids 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) suggested that organic acids could also be used for this purpose. These include, for example, oxalic acid, acetic acid, propionic acid, gluconic acid, tartaric acid or formic acid. In this context, the organic additive compounds include these and also nitric acid stabilizers as described below. The nitric acid stabilizer disclosed herein is used within the meaning of Campbell's US Patent 5,911,907. When mentioned in the composition of the etching solution of fresh or used tin or m tin lead they are referred to as "" anti-darkening agents ".

x, These compounds are added to prevent critical problems such as excessive consumption of HNC> 3 during treatment and to prevent the formation of exothermic conditions. Exothermic conditions include toxic NOx gas emissions from nitric acid in the presence of tin and copper ions and excessive copper etching. The concentration of the stabilizer should be about 5-30 g / l. Campbell described the general nature of "an organic additive containing nitrogen but no sulfur". More specifically, the stabilizer is an organic amine, preferably cyclic. Suitable nitric acid stabilizing agents are amino-triazole (preferably 4-amino-1,2,4-triazole). and 8 aminoisoxazole (preferably 3-amino-5-methylisoxazole) Other stabilizers disclosed in the patent literature (U.S. Patents 4,374,744, 5,512,201 and 5,911,907) include 4-amino-1,2 , 4-triazole, Ι, Ι, Γ, Γ-tetrakishydroxyethylenediamine, 1,2,3-triazole, 1,4-diazabicyclo-2,2,2-octane, 2,4-diamino-6-hydroxypyrimidine, 3,5 -di-5 amino-1,2,4-triazole, 3-amino-5-methylisoxazole, 4-amino antipyrin, 5-amino-3-methylisoxazole, alanine, benzotriazole, cyclohexylamine, diethanolamine, di- ethylenetriamine, ethylenediamine, glycine, hexamethylenetetramine, imidazole, indazole, indole, indolylacetic acid, monoethanolamine, naphthotriazole, N-ethyl substituted imid azole, N-methyl-substituted imidazole, propanolamine, propylene-10-diamidine, pyrazole hydrochloride, pyrazole, pyrazole carboxylic acid, pyrrole, pyrrolicarboxylic acid, triazole hydrochloride, triazole, triethanolamine, triethylenepaphenyl. Other additives containing both sulfur and nitrogen, such as 2-aminobenzenesulfonamide, 3-sulfamoyl-L-alanine, 4- (aminomethyl) benzenesulfonamide, 4-amino-6-chloro-1,3-benzenesulfonamide, 4-carboxy-15 benzenesulfonamide, amino-methanesulfonic acid, ammonium sulfamate, N- (2-thiazolyl) sulfanyl amide, sulfamethazine, sulfamide, methanesulfonamide, sulfanyl amide, sulfisomidine, sulfisoxazole and sulfadiazine.

By "conversion" of an organic compound is meant any reaction to an organic component in a waste solution that occurs during heating and subsequent changes in solubility, which may include polymerization, decomposition, oxidation, salt formation, or any other reaction typical of the compound. Depending on the solubility of the reaction product (s), the precipitation of the precipitates demonstrates how the above-described organic precipitate and SnC> 2 lose the 0 properties which considered them dispersed or dissolved and sink to the bottom of the reeked market.

V The object and benefit of the present invention will be described in more detail in the non-

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> - with the aid of limiting examples, with reference to the drawing.

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* 30 EXAMPLES

Two sets of examples were performed, the first set being run under normal atmospheric pressure and the second set running under pressure C 1.

9 EXAMPLE 1 The used tin etching solution, which was analyzed to contain 4% Sn, 24.4% NO 3, 0.9% organic C, 0.4% Cu and 1.6% Fe, was used in these experiments. a.

Effect of 5% HNO3 Addition at 60 and 85 ° C 5% by weight of 100% HNO3 was added to a sample of this spent tin etching solution and the mixture was stirred for 1 hour in a 1 liter glass reactor at 1 bar and 60 ° C. No clear layer was observed in the precipitation test. After heating at 60 ° C for a further two hours, the suspension precipitated over one day to give 79% v / v of the clear layer and 10 21% v / v of the precipitated SnCl 2.

To the sample of spent tin etching solution was added 5% by weight of 100% HNO 3 and the mixture was stirred for 1 hour in a 1 liter glass reactor at 1 bar and 85 ° C. During the reaction, some NOx gases were observed. In the precipitation test, the SnO2 suspension precipitated overnight to give 88% by volume of the clear layer and 12% by volume of the precipitated SnO2.

EXAMPLE 2. Effect of Higher Nitric Acid Additions at 80 ° C a) 0, b) 10, c) 20 and d) 30% by weight of 100% HNO3 was added to a sample of the spent tin etching solution and stirred for 1 hour in a 1 liter glass reactor. bar pressure and 80 ° C. In the precipitation test, the corresponding clear 20 layers after one day were a) 80% by volume, b) 80% by volume, c) 78% by volume, and d) 73.5% by volume. When 10-30% by weight of 100% HNO3 was added, a change to lighter 2 colors and NOx gases was observed.

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Ά EXAMPLE 3. Effect of 60-67 ° C and 75 ° C on Initially Used 25 Tin Etching Solution | A sample of the original spent tin etching solution, in which no nitric acid was added, was stirred in a 1 liter glass reactor at 1 bar pressure and 60 ° C for 1 hour 2 and an additional 1.5 hours at 67 ° C. In the precipitation test, SnO2 remained in suspension and did not precipitate.

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A sample of the original spent tin etching solution, in which no nitric acid was added, was stirred for 1 hour in a 1 liter glass reactor at 1 bar and 75 ° C. In the precipitation test, the SnO2 suspension precipitated overnight, yielding 10 to 81% by volume of the clear layer and 19% by volume of the precipitated SnO2.

EXAMPLE 4. 20-50 ° C and 2-20% ΗΝΟβίη Addition Has No Effect 5 When 2 or 5% by weight of 100% HNO3 was added to a sample of the tin etching solution and the mixture was stirred for 1 hour in a 1 liter glass reactor. and at 20 ° C, no precipitation occurred in the precipitate test. When 20% 100% HNO 3 was added and stirred for 1 hour in a 1 liter glass reactor at 1 bar and 28 or 50 ° C, no precipitation was observed in the pellet test.

10 Conclusions regarding tests carried out at a pressure of 1 bar:

The reaction which causes the precipitation of SnO2 starts at about 70 ° C for the spent tin etching solution alone and at about 60 ° C when 5% by weight of 100% HNC3 is added. The reaction did not take place at 50 ° C, although 20% HNO 3 was added. Higher nitric acid additions produce more NOx gases during the reaction. In these experiments, the calculated nitrate content is 24.4% by weight of NO3 to 41.8% by weight of NC> 3.

In all experiments, the combined liquid sample had a higher nitrate content than the original sample due to the addition of nitric acid, the same levels of copper, iron and organic carbon and much lower levels of tin. Tin is present as 20 SnO2 in both the original suspension and the precipitated sediments.

TESTS UNDER PRESSURE; EXAMPLE 5 o These experiments were carried out in a Parr titanium autoclave of 4563 model with a maximum volume of about 1000 ml. The reactor is equipped with a double four-blade rotor Ά, which is connected to the motor by magnetic coupling. The agitation speed ^ 25 was 300 rpm. A glass inner layer was used to protect the walls of the autoclave. Pressure was measured with a pressure gauge. An electric heat bath was used to heat the autoclave. At the end of the experiment, a cooled coil connected around the rotor cooled the solution. For temperature measurements, two K-type thermo

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The ria was inserted through a special opening in the autoclave. Another thermocouple was connected to a regulator 30 (heater) which controlled the electric heat bath. The setpoint temperature can be programmed into this controller. For comparison, another thermocouple was connected to a portable digital reader. After the reaction, the autoclave was cooled with water. The acidity and concentration of the final solution were determined after the contents of the autoclave had been removed.

The autoclave had a fill rate of about 70% (v / v). Before the reaction was completed, the reactor was purged with nitrogen gas to completely remove any oxygen gas remaining in the system.

The spent tin etching solution (700 mL) from a circuit board manufacturer was added to the reactor after the above preparations. The composition of the solution was about 12-15% (w / w) nitric acid, 5% (w / w) ferric ion Fe3 + or Fe2 + and trace amounts, <1% (w / w), anti-darkening agent and <1% suspension. -10 doughing agents, 2-15 g / l copper ion Cu2 + and about 10-120 g / l Sn4 + ion. The anti-darkening agent used in this context was benzotriazole.

The experiment was performed as described above. The temperature was initially 20 ° C and gradually increased to 210 ° C over a five hour reaction time. At the same time, the pressure increased from 1 bar to 15.2 bar.

After the autoclave treatment, the tin etching solution used was divided into two parts: a clear solution and a precipitate which settled on the bottom of the autoclave. The metal derivatives were distributed such that tin precipitated most (98% according to ICP analysis) and less than 2% remained in solution, whereas copper and iron derivatives remained in solution.

An important observation in the high pressure system was that NOx emissions were negligible. This is a significant advantage over the prior art.

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Claims (18)

A process for precipitating metal oxide (s) from a wastewater solution which is a spent etching solution of tin or tin lead and which wastewater solution additionally contains at least one inorganic acid, metal salts and / or complexes, and at least one organic additive, of which at least one additives comprise organic amine, in which process said aqueous solution is treated at an elevated temperature of 55-210 ° C for 1-30 hours, thereby providing a conversion of said organic additives to its precipitating derivative and a simultaneous precipitation of said metal oxide (s) ), wherein the treatment for converting said organic additive into its precipitated derivative is enhanced by the addition of nitric acid. The process of claim 1, wherein the organic amine in the wastewater solution is in the form of its site. The process of claim 2, wherein the anion of the organic amine site in the wastewater solution is in the form of halogen, advantageously in the form of chloride. 20 The process according to any of claims 1-3, wherein the organic amine is benzotriazole. The process according to any of claims 1-4, wherein the amount of organic amine is 0.2-5% (w / w), advantageously 0.5-2% (w / w) and most advantageously 0.5-1% (w / w) of the total weight of the wastewater solution. 2 The process of claim 3, wherein the amount of halogen which is advantageously in the form of its hydrogen halide is 0.2-2% (v / v), advantageously 0.5-2.0% 77 (v / v). ) of the entire wastewater solution. £ 30 A process according to any of claims 1-3, wherein the metal oxides comprise CL tin (IV) and / or lead (II) oxides. o g A process according to claims 1-7, wherein the amount of metal oxides is 1-300 g / l, advantageously 10-200 g / l and all most advantageously 50-180 g / l of the total volume of the wastewater solution. The method of claim 1, wherein the elevated temperature at atmospheric pressure is 68-100 ° C, advantageously 70-90 ° C and most preferably 70-85 ° C. 5 The method of claim 1, wherein the treatment for converting said organic additive into its precipitating derivative is effected by means of pressure. The method of claim 1, wherein the pressure is raised and it is 1-6 bar in a closed system during treatment. 10 The method of claim 11, wherein the elevated temperature is 70-210 ° C and advantageously 100-160 X. The method of claim 1, wherein said efficacy is performed by adding nitric acid prior to the treatment at elevated temperature. The process of claim 1 or 13, wherein the amount of nitric acid added is 2-20% (v / v), advantageously 5-10% (v / v) and most preferably 4.5-5.5% (v / v). . 20 The method of claim 1, further comprising recovering the recovered liquid phase at least partially back into an etching process of tin or tin lead. 25 The method of claim 1 or 14, comprising a further stage of further processing a liquid phase to utilize nitric acid, copper compounds, or iron compounds. o oy I; A process according to claim 15, wherein the copper content of the liquid phase is reduced to 30 by extraction, ion exchange, chemical reduction, eutectic crystallization in; or electrolytic enrichment. CL g The method of claim 1, wherein the solid phase contains over 70% tin of the initial total amount in the wastewater solution. O c \ l oo