JP2013155402A - Method of recovering zinc from waste galvanizing solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing economically recyclable high concentration zinc cake of a zinc concentration of at least 40%, by efficiently separating zinc present in a waste galvanization solution from iron at low cost.SOLUTION: A zinc composition including at least 40% of zinc per dry weight is recovered by an air-oxidation process of adding an alkali into a waste galvanizing solution comprising a zinc ion and a ferric ion each at least in a predetermined concentration and further comprising heavy metal to maintain its pH in a range of 4.5 to 5.5, blowing air thereinto to oxidize the ferric ion to a ferrous ion, and subsequently precipitating the ferrous ion as ferrous hydroxide; a first solid-liquid separation process of adding a chelating agent into the treated solution obtained and subsequently carrying out solid-liquid separation; a pH adjustment process of adding an alkali to the separated solution obtained to control its pH between 8 and 11 to precipitate zinc hydroxide; a second solid-liquid separation process of subjecting the treated solution obtained to solid-liquid separation; and washing the solid matter obtained.

Description

  The present invention relates to a method for separating and recovering zinc in a galvanizing waste liquid at a high concentration and high yield.

  The galvanizing waste liquid is a high concentration zinc-containing waste liquid generated in the galvanizing process on the steel material surface, and is assumed to be generated at 1 to 20,000 tons / year in Japan. Liquidity contains high-concentration zinc ions and iron ions eluted from steel in a 4-6 N high-concentration hydrochloric acid or sulfuric acid acidic solution. The zinc ion concentration includes several percent to 20 wt%, and the iron ion concentration includes several percent to 10 wt%. Zinc plating waste liquid is strongly acidic, requires a large amount of alkaline agent for neutralization, and is characterized by the presence of iron as divalent ions. Most of this waste liquid is treated as industrial waste, and after iron and zinc are neutralized, they are disposed of as a dehydrated cake of a mixed hydroxide of iron and zinc. Therefore, it seems that thousands of tons of zinc are discarded. Since the zinc concentration in the dehydrated cake is high, it is necessary to use it as a refining material for Yamamoto reduction and to recycle it. To achieve this economically, the concentration of coexisting iron and salt must be reduced as much as possible. Therefore, it is necessary to increase the zinc concentration to 40% or more. That is, a means for efficiently separating and recovering zinc from iron is required. Many methods are known as a separation and recovery technique from a waste liquid containing a plurality of metal ions. For example, in an iron-zinc system, Patent Document 1 discloses that a waste liquid containing various heavy metals such as a pickling waste liquid and a plating waste liquid of a steel plate is adjusted in a plurality of stages for each tank, and a hydroxide generation tendency due to pH. A method has been proposed in which the difference is used to deposit and separate a hydroxide for each metal type. Among these, as a method for oxidizing divalent iron, a method of adding iron-oxidizing bacteria is described. Patent Document 2 proposes a method for obtaining an iron cake having a low water content from a waste liquid in which a plurality of metals including iron are mixed. In this method, after divalent iron is oxidized to trivalent iron in a known manner in advance, It describes that a neutralizing agent is added to produce particles mainly composed of iron hydroxide (trivalent) at a pH of about 3 to 5. In Patent Document 3, for metal recovery from plating waste liquid sludge containing iron, zinc, etc., the sludge is dissolved in acid, and then ferrous iron (divalent iron) in the liquid is oxidized with an oxidizing agent such as hydrogen peroxide. A method has been proposed for obtaining a ferric precipitate by adjusting the pH after oxidation using a phosphine.

  In any of the above methods, iron is oxidized by some method, divalent iron is oxidized to trivalent iron, pH is adjusted thereafter, and separation and recovery from other coexisting metal components are achieved. Non-Patent Document 1 shows the effect of pH on the air oxidation rate of dilute iron with a dilute concentration of several mg / L to trivalent iron, and it is described that neutrality is suitable for oxidation. Yes.

JP 2003-7201 A JP 2005-296866 A JP 2007-237054 A

Yutaka Takai, Hiroshi Nakanishi, “Iron removal and manganese removal treatment of water”, Industrial Water Research Committee, 1987 P41.

  All of these methods utilize the feature that ferric hydroxide drastically reduces the solubility at pH 3 or higher in the tendency to form metal hydroxides.

  Chemical oxidation requires the addition of chemicals. In many cases, the cost of the chemicals to be added impairs the credits for recovering valuable metals and prevents the establishment of an economic process. The method using iron-oxidizing bacteria in Patent Document 1 is applied to a dilute solution having an iron ion concentration of several tens to several hundreds mg / L, although no oxidizing agent is added. There are no examples of application to waste liquids that contain high concentrations of iron ions, such as the high concentration of salt, and it is assumed that the activity of the fungus will be low. However, it is scientifically possible but not industrially feasible. Therefore, the present inventors added a predetermined amount of alkali to the sum of the molar amounts of iron and zinc in the galvanizing waste liquid, adjusted to a specific pH, and then blown air to divalent iron. Oxidizing ions into trivalent iron ions, depositing ferric hydroxide, separating from dissolved zinc, then adjusting pH again and depositing zinc to allow zinc cake to be transferred for a fee It was found that it can be recovered as a high-concentration zinc-containing composition or a valuable material that can be used for Yamamoto reduction, and a patent application was filed as Japanese Patent Application No. 2010-228243.

  However, the galvanizing waste liquid often contains heavy metals such as cadmium and lead, and these migrate into the iron cake obtained by separating ferric hydroxide. Iron cake has a low resource value and is usually landfilled as industrial waste. However, a new problem has been found that elution of these heavy metals may exceed landfill standards and may not be landfilled.

  The present invention has been made to solve such problems, and in the previous invention, by adding a chelating agent to the treatment liquid obtained by air oxidation, these precipitated with ferric hydroxide. The heavy metal is changed to an insoluble salt to suppress elution in the landfill process.

  That is, according to the present invention, zinc ions are contained at 10,000 mg / L or more and divalent iron ions are contained at 3,000 mg / L or more, and an alkali is added to a galvanizing waste solution containing heavy metals to adjust pH to 4.5. An air oxidation treatment step in which air is blown in while maintaining in the range of ~ 5.5 to oxidize divalent iron ions to trivalent iron ions and then precipitate as ferric hydroxide, and the air oxidation treatment step After adding a chelating agent to the treatment liquid obtained in step 1, a solid-liquid separation step is performed, and an alkali is added to the separation liquid obtained in the first solid-liquid separation step to adjust the pH to 8-11. Obtained in the second solid-liquid separation step and the second solid-liquid separation step in which the treatment liquid obtained in the pH adjustment treatment step is subjected to solid-liquid separation. Washed solids, zinc per dry weight A method of recovering zinc from a galvanizing waste solution, comprising a zinc recovery step of recovering a zinc composition containing 40% or more, and zinc ions of 10,000 mg / L or more and divalent iron ions of 3, While adding 000 mg / L or more and adding alkali to the galvanizing waste liquid containing heavy metal to maintain the pH in the range of 4.5 to 5.5, air was blown in, and divalent iron ions were converted into trivalent iron ions. An air oxidation treatment step in which iron oxide is oxidized and then precipitated as ferric hydroxide, and a first solid-liquid separation step in which solid-liquid separation is performed after adding a chelating agent to the treatment liquid obtained in the air oxidation treatment step. And a pH adjustment treatment step of adjusting the pH to 8 to 11 by adding an alkali and a sulfiding agent to the separation liquid obtained in the first solid-liquid separation step, and precipitating zinc hydroxide and zinc sulfide, and the pH Adjustment process A second solid-liquid separation step for solid-liquid separation of the treatment liquid obtained, and a solid composition obtained in the second solid-liquid separation step is washed to obtain a zinc composition containing 40% or more of zinc per dry weight. The present invention provides a method for recovering zinc from galvanizing waste liquid, characterized by comprising a recovery step of recovering zinc.

  According to the present invention, zinc in the galvanizing waste liquid can be recycled at a low cost and a high recovery rate, and the iron cake produced as a by-product can be stably landfilled. Moreover, it is not limited to a zinc plating waste liquid, It can utilize for the separation of iron or zinc from the waste liquid containing iron and zinc.

It is a flow sheet which shows the method of this invention. It is a graph which shows the relationship between pH of a liquid, Fe oxidation rate, and Zn recovery rate. It is a figure which shows the structure of a rubber membrane type diffuser.

  The galvanizing waste liquid to which the present invention is applied is a plating liquid produced when galvanizing iron plate, steel sheet, and other various steel materials by electrolytic plating, hot dipping, etc., waste liquid produced in the post-treatment of the plating process and the washing process. In a mineral acid such as hydrochloric acid or sulfuric acid of about 1 to 7 N, usually about 4 to 6 N, zinc ion is 10,000 mg / L or more, preferably 50,000 mg / L or more, more preferably 100,000 mg. / L or more, divalent iron ions are 3,000 mg / L or more, particularly 10,000 mg / L or more, and further contain heavy metals. Although the upper limit of zinc ion is not particularly limited, it is usually 200,000 mg / L or less, and most is 150,000 mg / L or less. The upper limit of the divalent iron ion is not particularly limited, but is usually 100,000 mg / L or less, and most is 60,000 mg / L or less. Examples of heavy metals include cadmium, lead, and the like. The content of heavy metal is not particularly limited, but is usually about several tens to several hundreds mg / L, particularly about 50 to 500 mg / L.

  The galvanizing waste liquid is diluted to about 2 to 6 times, preferably about 3 to 5 times while adding water and stirring as necessary. Dilution of galvanizing waste liquid improves the quality of the zinc cake. It is because the salt content accompanying the water | moisture content in a dewatering cake falls. In order to reduce the salt concentration present as a result of neutralization of the high concentration acid in the waste liquid, it is diluted to about 2 to 6 times. If the degree of dilution is increased too much, the quality will be improved, but the processing volume will be increased and the efficiency will be reduced.

  Next, an alkali is added to the diluted waste liquid to adjust to pH 4.5 to 5.5 and air is blown to oxidize divalent iron ions to trivalent iron ions. The apparatus for blowing air is not particularly limited, but it is desirable to use a rubber membrane type air diffuser. In the rubber membrane type air diffuser (FIG. 3), the air diffuser port is widened when ventilated, but the air diffuser port is closed when stopped, so that it is less likely to be blocked by the generated iron hydroxide particles. The pH conditions for air oxidation are preferably within a relatively narrow range of 4.5 to 5.5, preferably 4.6 to 5.4. It is known that the air oxidation of divalent iron in a low concentration range has a large pH dependence and a neutral range is preferable (Non-patent Document 1). However, in the case of the galvanizing waste solution targeted by the present invention, both iron and zinc are at high concentrations. Therefore, at pH 6 or higher, the oxidation of divalent iron proceeds, but the zinc coexists with the precipitation of ferric hydroxide. It sinks and the recovery rate of zinc falls. On the other hand, when the pH is 4 or less, the oxidation of divalent iron does not proceed, and divalent iron ions remain in the liquid and precipitate at the same time as zinc precipitation, so that the concentration of recovered zinc is lowered. Taking into account the oxidation rate of divalent iron and the zinc recovery rate, it was found that there is an optimum range for pH, which is around 5 (FIG. 2). There is no limitation on the type of alkali used for adjusting the pH, but it is preferable that it is inexpensive and can be obtained in large quantities, and examples include sodium hydroxide, sodium hydrogen carbonate, sodium carbonate, calcium oxide, calcium hydroxide and the like. Since the pH decreases with the progress of the air oxidation reaction and the oxidation reaction rate decreases with the decrease, the neutralizing alkali is continuously or intermittently added while monitoring the pH of the solution during the oxidation. It is better to maintain around 5 to 5.5. For example, when pH 5 is cut, an alkaline solution is added. By adjusting the pH slightly while oxidizing with air, it is possible to avoid the decrease in the oxidation rate caused by the decrease in pH accompanying the progress of the oxidation, and it is possible to add the alkali without excess or deficiency. At this time, there is a method in which the amount of alkali solution necessary for pH adjustment is determined in advance, and the addition of alkali is stopped when the amount of accumulated alkaline solution from the start of the air oxidation treatment reaches a predetermined amount of alkali. The required alkali amount is from 1/2 equivalent to equivalent to the sum of iron and zinc contained. Air oxidation is continued until the oxidation-reduction potential in the solution is monitored and the oxidation-reduction potential turns positive. When the oxidation time has a margin, it is desirable to continue until the oxidation-reduction potential reaches about +50 mV.

  The chelating agent is added at the final stage of the air oxidation treatment step because some heavy metal is taken into the solid phase of ferric hydroxide generated in the air oxidation process and insolubilized. By adding at the final stage, the amount of chelating agent added can be minimized. The chelating agent forms a chelate with a heavy metal such as cadmium or lead, and a dithiocarbamic acid-based, piperazine-based, or diethylamine-based one can be used. The addition amount of the chelating agent is about 0.2 to 2%, preferably about 0.5 to 2% with respect to the weight of the waste liquid.

  By this air oxidation, iron precipitates as ferric hydroxide. The means for separating the precipitate is not particularly limited, and various gravity filters, pressure filters, vacuum filters, and centrifuges can be used.

  In the separated cake, heavy metals such as cadmium and lead are insolubilized with a chelating agent in addition to ferric hydroxide, so these heavy metals are also included.

  Since the separation liquid after iron cake recovery has a high salt concentration, diluting before adding the alkali reduces the salt concentration in the liquid adhering to the cake when the zinc compound produced during the alkali addition is separated. Also, the solid-liquid separation property is improved.

  After completion of air oxidation, the filtrate separated into solid and liquid is then added with alkali to adjust the pH to about 8 to 11, preferably about 9.5 to 10.5, and precipitate zinc as a hydroxide. The alkali may be added all at once while confirming the pH, or may be added several times while confirming the formation state of the precipitate. In either case, the amount of alkali added is adjusted so that it finally falls within the pH range. The alkali used for pH adjustment is not particularly limited as long as the pH can be adjusted to this value, but sodium compounds such as sodium hydroxide, sodium hydrogen carbonate, sodium carbonate and the like are desirable because they are inexpensive and easily available. Neutralization with calcium hydroxide can also be performed, but in that case, the content of the recovered zinc cake is lowered. In addition to the method of precipitating as a hydroxide, a sulfurizing agent can be added and recovered as a sulfide. In this case, sodium sulfide such as sodium sulfide or sodium hydrogen sulfide is preferable as the sulfurizing agent to be added. When sodium hydrogen sulfide is added, the pH is lowered during the formation of zinc sulfide, so it is used in combination with the alkali. In this case, the addition condition of the sulfurizing agent is preferably added in the latter half of the neutralization with the alkali. This is because, due to the decrease in pH associated with the formation of zinc sulfide, hydrogen sulfide gas is likely to be generated when sodium hydrogen sulfide is added, and there is a possibility that it may be dangerous for workers. The addition start time of the sulfiding agent is specifically the time when the pH in the reaction solution becomes 5-6 or more by adding the alkali. The addition amount of the sulfurizing agent is suitably about 1 to 1.2 times equivalent (molar ratio) in terms of S equivalent to the amount of the remaining soluble zinc, that is, unreacted zinc. Here, the soluble zinc is zinc in the filtrate obtained by filtering the reaction solution with a 0.45 μm filter, and the value obtained by measuring the filtrate with an atomic absorption spectrometer or ICP emission spectrometer is the soluble zinc. It is defined as In the case where the addition of alkali is continued after the addition of the sulfiding agent, an amount of about 1 to 1.2 times equivalent (molar ratio) to the amount of soluble zinc remaining in the total amount of the sulfiding agent and the alkali is appropriate. After adding a necessary amount of alkali or sulfurating agent, the mixture is stirred for about 30 minutes to 1 hour, and then the precipitate is separated. At this time, if a flocculant such as a polymer flocculant is added, the separation can be promoted well, but it is not always necessary.

  After adding the flocculant, it is allowed to stand, remove the supernatant water, add water and stir, and repeat this to reduce the salt concentration in the zinc hydroxide or zinc sulfide cake obtained. it can. The separated supernatant water may be filtered with a filter press or the like after being transferred to another tank, or may be filtered with a filter press or the like before being transferred to another tank.

  The means for separating the precipitate is not particularly limited as in the case of the iron cake, and various gravity filters, pressure filters, vacuum filters, and centrifuges can also be used. In this dehydration step, the washing operation by directly adding water to the zinc cake can reduce the salt content in the cake in the same manner as the dilution of the plating stock solution described above, and is therefore effective in improving the purity of the zinc cake.

  In the present invention, the zinc concentration in the zinc cake needs to be 40% by weight or more, preferably 50% by weight or more by dry weight. For that purpose, (1) dilution by adding water before air oxidation of iron, (2 ) Dilution by adding water to the liquid from which the iron cake was separated, (3) Washing the separated zinc cake with water before dehydration, (4) Washing with water at the time of dehydration as appropriate, Is controlled so as to reduce the concentration of salt (such as NaCl) in the zinc cake. For these waters, water having a low salinity concentration, for example, industrial water, tap water, treated waste water having a low salinity concentration, or the like is used. The water content of the zinc cake dehydrated with a filter press is about 60 to 70% by weight.

  The separated cake contains zinc in a high concentration of 40% by weight or more. A zinc recovery process known in Yamamoto, for example, roasted and further purified as zinc oxide, dissolved in sulfuric acid and dissolved in zinc sulfate. It can be applied to a process of obtaining metallic zinc from a zinc sulfate solution by electrolysis.

  The solid-liquid separated filtrate can be further purified and discharged as needed, or reused as industrial water or the like. As a purification method, the precipitate is removed after pH adjustment. Depending on the water quality required at the time of reuse, the purification method can be combined with a reverse osmosis membrane method or the like.

A zinc plating waste solution 10L having a Zn ²⁺ concentration of 96,000 mg / L, an Fe ²⁺ concentration of 27,000 mg / L, a Cd ²⁺ concentration of 57 mg / L, and a Pb ²⁺ concentration of 270 mg / L was diluted three-fold with industrial water to obtain Zn A diluted waste solution having a ²⁺ concentration of 32,000 mg / L, an Fe ^{2+ of} 9,000 mg / L, a Cd ²⁺ concentration of 29 mg / L, a Pb ²⁺ concentration of 90 mg / L, a pH of 0.72, and an ORP448 mV was obtained. This diluted waste solution was divided into 200 ml portions and placed in a 500 ml tall beaker, and 20 (w / v)% NaOH was added under the conditions shown in Table 1 for air oxidation for 9 hours. Meanwhile, air was supplied using an air pump and an aeration bulb, and a stirrer was not used. In (1), NaOH was added at the start of the experiment to adjust the pH, and NaOH was added to pH 5 after 8.5 hours. (2) was added every 10 minutes using a micropipette. Since (3) had no precipitation, the stirrer was rotated and stirred only when NaOH was added.

各空気酸化処理液をろ紙Ｎｏ．５Ｃでろ過し、初流約５０ｍｌは除いて集めたろ紙を標準添加法で分析して表２の結果を得た。

Each air oxidation treatment solution is filtered with filter paper No. The filter paper collected by filtering with 5C, except about 50 ml of the initial flow, was analyzed by the standard addition method, and the results shown in Table 2 were obtained.

次に、空気酸化処理した亜鉛めっき廃液にキレート剤を添加してカドミウムと鉛の挙動を調べた。供試廃液の組成は、Ｚｎ２１０，０００ｍｇ／Ｌ、Ｆｅ６８，０００ｍｇ／Ｌ、Ｃｄ１１４ｍｇ／Ｌ、Ｐｂ５４０ｍｇ／Ｌであった。キレート剤には（エチレンアミノ）ジチオカルボキシナトリウム−エチレンベンジルアミン−エチレンアミン共重合体を使用した。実験条件と結果を表３に示す。

Next, the behavior of cadmium and lead was investigated by adding a chelating agent to the galvanizing waste solution subjected to air oxidation treatment. The composition of the test waste liquid was Zn 210,000 mg / L, Fe 68,000 mg / L, Cd 114 mg / L, Pb 540 mg / L. As the chelating agent, (ethyleneamino) dithiocarboxy sodium-ethylenebenzylamine-ethyleneamine copolymer was used. The experimental conditions and results are shown in Table 3.

  According to the present invention, zinc can be recovered from zinc plating waste liquor with high purity and reused, and the processing load of the waste liquor can be reduced.

Claims (4)

  The pH is in the range of 4.5 to 5.5 by adding alkali to a zinc plating waste solution containing zinc ions of 10,000 mg / L or more and divalent iron ions of 3,000 mg / L or more and further containing heavy metals. The air oxidation treatment step of blowing air and oxidizing the divalent iron ions into trivalent iron ions and then precipitating them as ferric hydroxide, and the treatment liquid obtained in the air oxidation treatment step After adding a chelating agent to the first solid-liquid separation step of solid-liquid separation, and adjusting the pH to 8-11 by adding alkali to the separation liquid obtained in the first solid-liquid separation step, The pH adjustment treatment step for precipitating zinc, the second solid-liquid separation step for solid-liquid separation of the treatment liquid obtained in the pH adjustment treatment step, and the solid matter obtained in the second solid-liquid separation step are washed. And contain 40% or more of zinc per dry weight Zinc recovery process from galvanized waste, characterized in that it comprises a zinc recovery process for recovering the lead composition.   The method for recovering zinc from the galvanizing waste liquid according to claim 1, wherein water is added to the galvanizing waste liquid to dilute it 2 to 6 times, and then the air oxidation treatment is performed.   The pH is in the range of 4.5 to 5.5 by adding alkali to a zinc plating waste solution containing zinc ions of 10,000 mg / L or more and divalent iron ions of 3,000 mg / L or more and further containing heavy metals. The air oxidation treatment step of blowing air and oxidizing the divalent iron ions into trivalent iron ions and then precipitating them as ferric hydroxide, and the treatment liquid obtained in the air oxidation treatment step After adding the chelating agent to the first solid-liquid separation step for solid-liquid separation, and adjusting the pH to 8 to 11 by adding alkali and sulfiding agent to the separation liquid obtained in the first solid-liquid separation step Obtained in the second solid-liquid separation step, the second solid-liquid separation step for solid-liquid separation of the treatment liquid obtained in the pH adjustment treatment step, and the pH adjustment treatment step for depositing zinc hydroxide and zinc sulfide. Wash the solids and dry The zinc recovery process from galvanized waste, characterized in that it comprises a zinc recovery process for recovering zinc composition containing 40% or more.   The method for recovering zinc from the galvanizing waste liquid according to claim 3, wherein water is added to the galvanizing waste liquid to dilute it 2 to 6 times, and then the air oxidation treatment is performed.

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