WO2021147814A1 - 一种硫酸锌溶液中氢氧根浓度的测定方法 - Google Patents

一种硫酸锌溶液中氢氧根浓度的测定方法 Download PDF

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WO2021147814A1
WO2021147814A1 PCT/CN2021/072464 CN2021072464W WO2021147814A1 WO 2021147814 A1 WO2021147814 A1 WO 2021147814A1 CN 2021072464 W CN2021072464 W CN 2021072464W WO 2021147814 A1 WO2021147814 A1 WO 2021147814A1
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solution
concentration
zinc sulfate
acid
volume
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张旭
张云彭
耿惠
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昆明瀚创科技有限公司
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
    • G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration

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  • the invention belongs to the field of analytical chemistry and non-ferrous metal metallurgy, and mainly relates to a method for determining the composition of a neutral zinc sulfate solution in the production process of hydrometallurgy of zinc and zinc, and specifically relates to a method for determining the concentration of hydroxide radicals in a neutral zinc sulfate solution.
  • the measuring method instead of measuring the pH of the solution, is used to control the composition of the neutral solution during the leaching and purification process.
  • the zinc hydroxide in the solution is in a saturated state, and the combination of zinc hydroxide and zinc sulfate leads to a large amount of basic zinc sulfate. Due to the fine particle size of this species, the amount of purified residue is large and it is difficult to filter. In order to solve this problem, the industry often uses a small amount of sulfuric acid to dissolve the hydroxide in the solution. However, due to the lack of targeted quantitative detection methods in the solution, the amount of acid added cannot be accurately controlled. If the amount of acid added is too much, the solution will be acidified. , That is, the solution is in an acidic environment, which affects the process. The amount of acid added is too small to achieve satisfactory process results.
  • Chinese patent CN201410807515.2 discloses a method for reducing the consumption of zinc powder when replacing copper and cadmium by adjusting the pH of the pre-replacement solution to 1 to 4.5.
  • the pH of the pre-replacement solution is adjusted by adding sulfuric acid or electrolyte waste.
  • the zinc powder for replacing copper and cadmium can be reduced by more than 50%, but this method does not provide a basis for the amount of acid added.
  • this method does not provide a basis for the amount of acid added.
  • only controlling the pH of the front solution is not sufficient to provide a basis for adding acid.
  • Chinese patent CN102492842A discloses a method and device for measuring and controlling the BT value of a solution during the purification process of arsenic salt.
  • the method for measuring the BT value is to take a purified slurry and filter and measure out 25ml of filtrate, then add 25ml of distilled water, and drop 2 ⁇ 4 drops of methyl orange, titrated with 10g/L sulfuric acid solution, until the solution turns red, the number of milliliters of sulfuric acid solution used is the BT value.
  • the BT value described in the present invention cannot accurately characterize the essence of basic zinc sulfate in the purification process. This method of determination does not consider the change in the titration end point caused by the change of zinc ions in the solution. It is only proposed for the special process of arsenic salt purification. This is an approximate measurement parameter, and this measurement method has not been reported in other processes.
  • the US patent US8021459B2 discloses a method and instrument for separating impurities in the purification process of zinc sulfate. It mentions that the BT (Back Titration) value is a back titration value, and its purpose is to control the concentration of basic zinc sulfate in the solution to prevent the zinc powder from passivating. change.
  • BT Back Titration
  • the purpose of the present invention is to:
  • pH control method for the neutral zinc sulfate solution in the purification process of hydrometallurgical zinc smelting provides a method for determining the hydroxide radical in the zinc sulfate solution produced during the purification process, which is a neutral zinc sulfate solution Provide a basis for the control of ingredients.
  • a method for determining the hydroxide concentration in a zinc sulfate solution which is characterized in that: take a certain amount of hot filtered zinc sulfate solution, add an appropriate amount of distilled water, insert a pH electrode in the zinc sulfate sample solution and water In the mixture; after stirring uniformly, use a standard acid with a calibrated H + concentration to slowly add the OH- concentration in the zinc sulfate solution, and keep stirring during the titration; record the volume and pH change curve of the added standard acid until the pH of the solution is less than 3.5; and The equivalence point of the titration is judged by the first-order differential curve of the added volume of the standard acid and the pH of the solution, and the OH - concentration of the solution is calculated using the standard acid consumed at the equivalence point.
  • the volume of the certain amount of hot filtered solution is 5-50ml, the amount of distilled water added is 50-100ml, and the stirring is by magnetic stirring.
  • the method for measuring the hydroxide concentration in the zinc sulfate solution is characterized in that the standard acid is sulfuric acid or hydrochloric acid, preferably hydrochloric acid.
  • the method for measuring the hydroxide concentration in the zinc sulfate solution is characterized in that: the standard acid concentration is prepared with hydrochloric acid and distilled water, the hydrochloric acid purity is at least analytically pure, and the concentration in terms of H + is 0.1-0.3 mol/ L. After mixing, the H + concentration of the prepared aqueous hydrochloric acid solution is calibrated by a known method, and the hydrochloric acid aqueous solution with the calibrated concentration is the standard acid.
  • the slow acid addition is slowly adding within 10 minutes.
  • the method for determining the hydroxide concentration in the zinc sulfate solution is characterized in that: the volume V of the added standard acid and the change of the pH of the solution are recorded and the pH-V curve is drawn, and the pH-V curve is calculated and drawn according to the drawn pH-V curve.
  • the first-order numerical differential curve of ⁇ V-V takes the standard acid volume corresponding to the maximum value of ⁇ pH/ ⁇ V on the first-order numerical differential curve as the equivalence point; the record adds the volume of standard acid and the pH of the solution are controlled by computer
  • the titrator automatically records, the first-order differential curve is also automatically calculated by the computer, and the titration equivalence point is also automatically judged by the automatic titrator.
  • the method for measuring the hydroxide concentration in the zinc sulfate solution is characterized in that the hot filtration is performed at a temperature of 70-90°C, preferably 80-90°C.
  • the method for determining the hydroxide concentration in the zinc sulfate solution is characterized in that: the titration temperature is room temperature.
  • the method for determining the OH - concentration is: take 5-50ml of zinc sulfate solution hot filtered at 80-90 degrees, add 50-100ml of distilled water, use 0.1-0.3mol/l hydrochloric acid with a calibrated concentration, slowly under stirring Add the solution until the pH of the solution is less than 3.5; record the standard acid consumption volume and the change of the pH of the solution and plot the recorded titration volume-pH into a graph, calculate and plot the first-order value of ⁇ pH/ ⁇ V-V according to the recorded curve
  • the standard acid volume corresponding to the maximum value of ⁇ pH/ ⁇ V-V on the first-order numerical differential curve is taken as the equivalence point; and the volume of the solution is calculated based on the volume of the standard acid consumed by the equivalence point OH - concentration.
  • the inventor’s research also shows that after cooling the sample to room temperature, OH - exists in the form of basic zinc sulfate precipitated as a solid and partially dissolved zinc hydroxide, and basic zinc sulfate is a solid that cannot be ionized, forming a solid-liquid two-phase buffer Therefore, the zinc hydroxide concentration change of the sample cannot be characterized by the pH measurement method of the sample after cooling to normal temperature.
  • the response is:
  • Reaction (1) leads to an increase in the amount of slag and difficulty in filtering.
  • adding sulfuric acid can dissolve the basic zinc sulfate, but how to add an appropriate acid to maintain the activity of the zinc powder and avoid excessive zinc powder consumption, the key is The amount of acid added is controlled, and the basis of the control lies in the determination of the concentration of hydroxide in the solution.
  • Pure acid-base titration is a classic chemical reaction.
  • the pH of the equivalence point of the titration is related to the concentration of zinc ions in the solution.
  • the concentration of zinc sulfate liquid often changes, as well as the amount of water added to the titration solution and the amount of standard acid added will affect the titration equivalence point, which is the difficulty in titrating the hydroxide in the zinc sulfate solution.
  • the pH of the solution basically does not change. Only when the hydroxide in the solution is completely consumed by the added standard acid solution, the titration solution The pH will change drastically, and this drastic change can be obtained by using the standard acid volume and pH change curve.
  • the zinc concentration of the solution will affect the equivalence point of the titration, that is, the higher the zinc ion concentration in the titration solution, the higher the equivalence point pH of the titration, and an accurate titration end point cannot be obtained by controlling the end point of the titration with a constant pH.
  • the inventor proposed to record the volume of the standard acid and the change of the pH of the solution, and draw a curve of the added volume and pH of the standard acid, and then perform a first-order numerical differentiation on the drawn curve, that is, the ⁇ pH/ ⁇ V-V curve .
  • a curve of the added volume and pH of the standard acid that is, the ⁇ pH/ ⁇ V-V curve .
  • there is basically no change in pH indicating that Zn 2+ in the sample, solid Zn(OH) 2 ZnSO 4 .xH 2 O and OH - in the solution constitute a buffer system.
  • the acid dissolves the sample.
  • the solution turns acidic, and the OH - in the solution is neutralized by all the acid. There is no OH -in the solution, only H + .
  • the maximum point of the first-order numerical differential is selected.
  • the pH electrode as the indicator electrode, slowly add the standard acid under constant stirring at room temperature and record the change curve of the added volume of the standard acid and the pH of the solution, that is, the pH-V curve, and then perform the first-order numerical differentiation according to the curve.
  • the invention can be used to control the components of the neutral zinc sulfate solution in any stage of the hydrometallurgical zinc smelting.
  • Figure 1 shows the pH-V curve and ⁇ pH/ ⁇ V-V of Example 1, where a is pH-V, b is ⁇ pH/ ⁇ V-V, and c is the equivalence point (EP1) of the titration.
  • Figure 2 shows the pH-V curve and ⁇ pH/ ⁇ V-V of Example 2, where a is pH-V, b is ⁇ pH/ ⁇ V-V, and c is the equivalence point (EP1) of the titration.
  • Figure 3 shows the pH-V curve and ⁇ pH/ ⁇ V-V of Example 3, where a is pH-V, b is ⁇ pH/ ⁇ V-V, and c is the equivalence point (EP1) of the titration.
  • Fig. 4 shows the pH-V curve and ⁇ pH/ ⁇ V-V of the base concentration for calibration in Example 4, where a is pH-V, b is ⁇ pH/ ⁇ V-V, and c is the equivalence point (EP1) of the titration.
  • Fig. 5 shows the pH-V curve and ⁇ pH/ ⁇ V-V of the standard acid for calibration and titration in Example 4, where a is pH-V, b is ⁇ pH/ ⁇ V-V, and c is the equivalence point (EP1) of the titration.
  • Example 1 This example is the determination of the alkalinity of the liquid after the two-stage nickel and cobalt removal.
  • the composition of the solution is Zn 150g/L, Co 0.025mg/L, Ni 0.03mg/L, Ge 0.015mg/L, Cd 0.15mg/L, take 20ml of hot filtrate, add water to 40ml, use the calibrated HCl solution, the actual A concentration of 0.2404mol/L is slowly dripped into the measurement sample as a titrant, and titrated until the pH reaches below 2, record the addition volume of standard acid and the change in pH of the solution, and draw the recorded addition volume and pH of the standard acid into a pH-V curve, according to Calculate and draw the first-order numerical differential curve of ⁇ pH/ ⁇ V-V for the recorded curve, and take the maximum value of the first-order numerical differential as the equivalence point.
  • the graph drawn is shown in Figure 1, where the titration of the first-order numerical differential is obtained
  • the equivalence point volume is 2.1785ml
  • the corresponding equivalence point is EP1 shown in the standard acid volume pH-V change chart
  • the equivalence point pH is 4.27.
  • the equivalence point volume and concentration are calculated and the OH - concentration of the solution is 0.0262mol/L.
  • the titration is about 10 minutes from start to end.
  • Example 2 This example is the determination of the alkalinity of the solution in the neutral leaching process.
  • the components of the solution are Zn 170g/L, Co 0.08mg/L, Ni 0.02mg/L, As 0.15mg/l, Sb 0.19mg/l , Ge 0.15mg/L, Cd 500mg/L, take 10ml of hot filtrate, add 30ml of water, use the HCl solution with the calibrated concentration, the calibrated H + concentration of 0.1107mol/L as the titrant, slowly drip into the measurement sample, and titrate
  • the pH is about 3
  • record the standard acid consumption volume and the change in pH of the solution and plot the recorded titration volume and pH into a pH-V diagram calculate and plot the first-order numerical differential curve of ⁇ pH/ ⁇ V-V based on the recorded curve, and The standard acid volume corresponding to the maximum value of the first-order numerical differential is used as the equivalence point.
  • the graph drawn is shown in Figure 2.
  • the titration equivalence point volume obtained by the first-order numerical differential in the figure is 2.9035ml, and the corresponding equivalence point It is EP1 shown in the standard acid volume-pH change diagram, and the equivalence point pH is 5.02.
  • the equivalence point volume and concentration are calculated and the OH - concentration of the solution is 0.0321mol/L.
  • the titration is about 10 minutes from start to end.
  • Example 3 This example is the determination of the alkalinity after a period of post-liquid adjustment.
  • the solution components are Zn 140g/L, Co 6mg/L, Ni 5mg/L, Ge 0.13mg/L, Cd 80mg/L, take Hot filtrate 40ml, add water 30ml, use the calibrated HCl solution, the actual concentration is 0.1107mol/L as the titrant, slowly drip into the measurement sample, titrate to about pH3.8, record the standard acid consumption volume and the change of solution pH and The recorded titration volume and pH are plotted as a pH-V graph, and the ⁇ pH/ ⁇ V-V first-order numerical differential curve is calculated and drawn according to the recorded curve.
  • the standard acid volume corresponding to the maximum value of the first-order numerical differential is equal to
  • the graph is drawn as shown in Figure 3, the first-order numerical differentiation in the figure obtains a titration equivalent point volume of 0.4060ml, and an equivalent point pH of 4.42.
  • the equivalence point volume and concentration are calculated and the OH - concentration of the solution is 0.0045mol/L.
  • the titration is about 10 minutes from start to end.
  • Embodiment 4 is the standard acid used in the calibration experiment (ie, the H + concentration of the prepared aqueous hydrochloric acid solution is calibrated by a known method), and it is implemented with reference to the national standard GB/T601-2003. This method uses two calibrations, the first time the concentration of the standard alkali is calibrated, and then the calibrated alkali standard solution of known concentration is used to calibrate the said standard acid.
  • An example of the calibration of the lye is: drying the standard potassium hydrogen phthalate standard substance at 105 ⁇ 110°C to a constant weight, dissolving 110g sodium hydroxide in 100ml carbon dioxide-free water, and placing it in a sealed polymer Place in an ethylene container until the solution is clear, take 10.8ml of the upper clear solution, add water and dilute to 1000ml to prepare sodium hydroxide titrant.

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Abstract

一种中性硫酸锌溶液中氢氧根浓度的测定方法，取一定量的经热过滤的硫酸锌溶液，并加入适量的蒸馏水；搅拌均匀后，采用标准酸缓慢加入硫酸锌溶液中，滴定过程不断搅拌；记录加入标准酸体积和pH的变化曲线，直至溶液pH小于3.5，通过标准酸加入体积和溶液pH的一阶微分曲线判断滴定等当点，采用等当点消耗的标准酸计算溶液的氢氧根浓度。该方法用于湿法炼锌生产过程中性硫酸锌液成分的控制。

Description

一种硫酸锌溶液中氢氧根浓度的测定方法 技术领域
本发明属分析化学和有色金属冶金领域，主要涉及一种湿法炼锌锌生产过程中性硫酸锌溶液的成分测定方法，具体地说是涉及一种中性硫酸锌溶液中氢氧根浓度的测定方法，替代测量溶液pH，用于浸出和净化过程中中性溶液成分的控制。
背景技术
在电解锌厂硫酸锌溶液的净化过程中，大量的研究及生产实践表明，在净化过程中锌粉加入后易产生大量的碱式硫酸锌，使得锌粉钝化，影响净化特别是除钴效果，同时导致溶液中产生大量碱式硫酸锌，此外，采用锑盐净化除镍钴的过程中，一般仅是在前液加入少量硫酸调整溶液的pH，过程中仅靠溶液的pH进行控制，在实际生产中，由于缺乏检测手段，溶液中的氢氧化锌处于饱和状态，氢氧化锌和硫酸锌结合导致大量碱式硫酸锌产生。由于该物种粒度细，使得净化渣量大，过滤困难。为了解决这一问题，工业上常采用加入少量硫酸溶解溶液中的氢氧化物，但由于缺乏溶液中针对性的定量检测手段，无法准确控制加酸量，加酸量过多时将导致溶液的酸化，即溶液处于酸性环境，使工艺过程受到影响。加酸量过少又不能达到满意的工艺效果。
中国专利CN201410807515.2的公开了一种通过调整置换前液中的pH为1～4.5的来降低置换铜镉时锌粉耗量的方法，通过加入硫酸或电解废液调整置换前液的pH，可使得置换铜镉的锌粉降低50％以上，但此方法未提供加酸量的依据，实际置换过程中，特别是置换除铜镉过程仅控制前液的pH不足以提供加酸依据。
中国专利CN102492842A公开了一种砷盐净化过程中测量及控制溶液的BT值的方法及装置，其测量BT值的方法为取净化料浆过滤后量出25ml滤液，再加入25ml蒸馏水，滴入2～4滴甲基橙，采用10g/L的硫酸溶液滴定，至溶液变红为止，所使用的硫酸溶液毫升数为BT值。该发明所述的BT值不能准确表征净化过程碱式硫酸锌的本质，这一测定方式也未考虑溶液中锌离子变化导致的滴定终点发生变化的问题，仅是针对砷盐净化的特殊工艺提出的一种近似的测量参数，该测定方法未见在其它工艺过程中应用的报道。
美国专利US8021459B2公开了一种硫酸锌净化过程中分离杂质的方法及仪器，其中提及BT(Back Titration)值为反滴定值，其目的也是控制溶液中的碱式硫酸锌的浓度防止锌粉钝化。
对于这一类溶解了少量氢氧化物的中性硫酸锌溶液，一直未能找到一种替代pH的测量方法。生产实践和研究均需要一种中性硫酸锌液体中OH -浓度的测定方法，为控制湿法炼锌中性硫酸锌溶液中的成分提供依据。
发明内容：
针对上述专利和公开技术的不足，本发明的目的在于：
为湿法炼锌净化过程中性硫酸锌溶液提供一种替代pH控制的方法，具体的说是提供一种净化过程中产出硫酸锌溶液中氢氧根的测定方法，为中性硫酸锌溶液的成分控制提供依据。
具体测定过程技术方案如下：
一种硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：取一定量的经热过滤的硫酸锌溶液，并加入适量的蒸馏水，插入pH电极在所述的硫酸锌样品溶液和水的混合物中；搅拌均匀后，采用已标定H +浓度的标准酸缓慢加入硫酸锌溶液中的OH -浓度，滴定过程不断搅拌；记录加入标准酸体积和pH的变化曲线，直至溶液pH小于3.5；并且滴定等当点采用标准酸加入体积和溶液pH的一阶微分曲线判断，采用等当点消耗的所述的标准酸计算溶液的OH -浓度。
所述一定量热过滤溶液的体积是5～50ml，加入蒸馏水的量是50～100ml，所述的搅拌是采用磁力搅拌。
所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述标准酸为硫酸、盐酸，优选盐酸。
所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述的标准酸浓度采用盐酸和蒸馏水配制，盐酸纯度至少为分析纯，以H +计的浓度为0.1～0.3mol/L，混匀后采用公知的方法对所配制的盐酸水溶液的H +浓度进行标定，标定浓度的盐酸水溶液即为所述的标准酸。
所述的采用已标定浓度的盐酸缓慢加入滴定硫酸锌溶液中的OH -浓度的方法，所述的缓慢加酸是在10分钟内缓慢加入。
所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：记录加入标准酸 体积V和溶液pH的变化并绘制pH-V曲线，根据所绘制的pH-V曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分曲线上ΔpH/ΔV的最大值对应的标准酸体积作为等当点；所述的记录加入标准酸体积和溶液pH是采用计算机控制的滴定仪自动记录，所述的一阶微分曲线也为计算机自动计算，滴定等当点也为所述的自动化滴定仪自动判断。
所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述热过滤是在温度70～90℃下进行，优选80～90℃。
所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述滴定温度为室温。
所述OH -浓度的测定方法为：取5～50ml在80～90度下热过滤的硫酸锌液，加入50～100ml蒸馏水，采用0.1～0.3mol/l标定出浓度的盐酸，在搅拌下缓慢加入所述的溶液，直至溶液的pH小于3.5；记录标准酸消耗体积和溶液pH的变化并将记录的滴定体积-pH绘制成图形，根据所记录曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分曲线上ΔpH/ΔV-V的最大值对应的标准酸体积作为等当点；并且根据等当点所消耗的所述的标准酸消耗的体积计算溶液的OH -浓度。
为了进一步说明本发明机理，发明人对上述过程进行进一步说明。
在湿法炼锌生产中，硫酸锌的中性溶液，通常溶解了少量的氢氧化物，主要是氢氧化锌，本发明人认为：溶液中的OH -和硫酸锌溶液和渣中的碱式硫酸锌构成了一个复杂的pH缓冲体系，使得溶液的pH基本不发生变化，导致采用测量溶液的pH值不能表征溶液的特性，采用测量溶液pH值作为控制生产工艺过程的依据存在不足。
生产实践及研究均发现，将热的硫酸锌净化滤液冷却后，会出现大量白色的沉淀物，这些沉淀物为碱式硫酸锌。这说明溶液中氢氧化锌在硫酸锌溶液中具有一定溶解度，温度越高，溶解度越大，在一定温度下，如果溶液中的氢氧化锌浓度达到饱和，进而和硫酸锌液中的锌离子结合形成碱式硫酸锌沉淀引起锌粉的钝化。本发明人的研究还表明，冷却样品至常温后，OH -以固体析出的碱式硫酸锌和部分溶解的氢氧化锌形式存在，碱式硫酸锌为固体无法电离，形成固-液二相缓冲体系，故样品的氢氧化锌浓度变化无法用冷却至常温后的样品pH测量方法 表征。
其反应为：
Zn(OH) 2+ZnSO 4+xH 2O＝Zn(OH) 2ZnSO 4.xH 2O   (1)
反应(1)导致渣量增加，过滤困难，显然加入硫酸可以将所述的碱式硫酸锌溶解，但如何加入适当的酸，既保持锌粉的活性，又避免过量锌粉的消耗，关键在于加酸量的控制，而控制的基础在于溶液中氢氧化物浓度的测定。
纯的酸碱滴定为经典的化学反应，理论滴定的等当点pH为7，但在测定含易水解盐的溶液中游离酸时，滴定到pH＝7时，直接导致金属盐水解而不能获得游离酸数值。对于游离碱的滴定由于易水解的金属离子存在，不能将滴定等当点定为pH＝7时。研究表明，溶液中含有少量氢氧化锌，采用酸直接滴定不能获得准确的结果，要准确滴定硫酸锌溶液中的OH -，确定滴定等当点是准确滴定的关键。而滴定等当点的pH又和溶液中的锌离子浓度相关，为了准确测定溶液中的OH -，必须控制滴定等当点处于滴定液中的锌等金属离子不发生水解的pH，但在实际生产过程中，硫酸锌液体浓度经常发生变化，以及滴定液中加入的水量及加入标准酸的数量都将影响滴定等当点，这是滴定硫酸锌溶液中氢氧化物的难点。
在滴定游离碱时发生的反应如下：
OH -+H +＝H 2O   (3)
在滴定过程中根据溶度积原理，建立了如下平衡关系：
Zn 2++2OH -＝Zn(OH) 2   (4)
在滴定过程中，当溶液中还存在氢氧化物或碱式硫酸锌时，溶液的pH基本不发生变化，只有当溶液中的氢氧化物完全被加入的标准酸溶液消耗完后，滴定液的pH才会出现剧烈变化，这种剧烈变化可采用标准酸体积和pH变化曲线获得。
由于溶度积Ksp Zn(OH)2＝[Zn 2+]×[OH -] 2在一定含锌溶液中为一固定值，溶液锌浓度较高时，则滴定等当点pH较高，而溶液浓度较低时，则滴定等当点pH较低，而等当点溶液中的锌浓度取决于样品带入的锌和样品体积、标准酸体积和加水体积三者的总体积的比值。显然，溶液的锌浓度将影响到滴定的等当点，即滴定液中锌离子浓度越高，滴定的等当点pH也越高，采用定pH控制滴定终点不能获得准确的滴定终点。
为了解决这个问题，本发明人提出采用记录标准酸体积和溶液pH的变化， 并绘制标准酸加入体积和pH变化曲线，再对所绘制的曲线进行一阶数值微分，即ΔpH/ΔV-V曲线。在滴定接近等当点前pH基本无变化，说明样品中Zn 2+与固体Zn(OH) 2ZnSO 4.xH 2O和溶液中的OH -构成缓冲体系，在这一阶段是酸溶解样品中的Zn(OH) 2ZnSO 4.xH 2O或氢氧化锌，由于这些碱性物质的存在构成了pH缓冲体系，pH基本无变化。接近等当点时，溶液中的氢氧化物耗尽，加入的酸使溶液pH剧烈下降，这种剧烈变化可通过记录滴定标准酸加入体积和溶液的pH变化曲线，并对该曲线采用一阶数值微分对该曲线进行处理得到，一阶数值微分曲线的最大值点即为滴定的等当点，在该等当点之前，溶液为碱性，此时溶液中还存在未反应的OH -，等当点之后溶液转为酸性，溶液中的OH -被全部酸中和，溶液中不存在OH -，只存在H +，根据相关数学理论，选取所述的一阶数值微分的最大值点即为溶液由碱性转为酸性的点，也即为滴定的等当点，该等当点对应的标准酸体积即为滴定OH -消耗的标准酸的数量。具体的做法是采用pH电极为指示电极，在常温、不断搅拌下缓慢加入标准酸并记录标准酸加入体积和溶液pH的变化曲线，即pH-V曲线，再根据该曲线进行一阶数值微分，得到一阶数值微分和标准酸体积的变化曲线，即ΔpH/ΔV-V曲线，取一阶数值微分值最大点对应的标准酸积为滴定等当点，再根据等当点消耗的酸液体积和样品溶液体积即可计算出样品的OH -浓度，OH -浓度＝(等当点消耗的标准酸体积×标准酸的H +浓度)/样品体积。显然采用人工记录和计算所述的曲线是一个不可能完成的任务，而采用计算机控制的自动电位滴定仪则可完成这一任务，本发明是采用瑞士万通的Titrando 809自动电位滴定仪完成的。
本发明可用于湿法炼锌任意一个阶段的中性硫酸锌溶液成分的控制。
本发明产生的有益效果：
通过准确测定硫酸锌溶液中的OH -浓度，为湿法炼锌过程中性硫酸锌溶液的控制提供一种替代溶液pH控制的参数，对工艺优化及过程稳定控制提供了依据。
附图说明
图1为实施例1的pH-V曲线和ΔpH/ΔV-V，其中a为pH-V，b为ΔpH/ΔV-V，c为滴定的等当点(EP1)。
图2为实施例2的pH-V曲线和ΔpH/ΔV-V，其中a为pH-V，b为ΔpH/ΔV-V，c为滴定的等当点(EP1)。
图3为实施例3的pH-V曲线和ΔpH/ΔV-V，其中a为pH-V，b为ΔpH/ΔV-V，c为滴定的等当点(EP1)。
图4为实施例4中标定滴定用碱浓度的pH-V曲线和ΔpH/ΔV-V，其中a为pH-V，b为ΔpH/ΔV-V，c为滴定的等当点(EP1)。
图5为实施例4中标定滴定标准酸的pH-V曲线和ΔpH/ΔV-V，其中a为pH-V，b为ΔpH/ΔV-V，c为滴定的等当点(EP1)。
具体实施方式
实施例1：此实施例为二段除镍钴后液的碱化度测定。溶液成分为Zn 150g/L，Co 0.025mg/L，Ni 0.03mg/L，Ge 0.015mg/L，Cd 0.15mg/L，取热过滤液20ml，加水至40ml，使用经标定的HCl溶液，实际浓度为0.2404mol/L作为滴定剂缓慢滴入测定样品，滴定至pH达到2以下，记录标准酸加入体积和溶液pH的变化并将记录的标准酸加入体积和pH绘制成pH-V曲线，根据所记录曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分的最大值作为等当点，所绘制的图形如图1，图中一阶数值微分的得到滴定等当点体积为2.1785ml，相应的等当点为标准酸体积pH-V变化图中所示的EP1，此等当点pH为4.27。等当点体积与浓度进行计算得到溶液的OH -浓度为0.0262mol/L。滴定从开始到结束约为10分钟。
实施例2：此实施例为中性浸出过程溶液的碱化度测定，溶液成分为Zn 170g/L，Co 0.08mg/L，Ni 0.02mg/L，As 0.15mg/l，Sb 0.19mg/l，Ge 0.15mg/L，Cd 500mg/L，取热过滤液10ml，加水30ml，使用经标定出浓度的HCl溶液，标定的H +浓度为0.1107mol/L作为滴定剂缓慢滴入测定样品，滴定至pH约为3，记录标准酸消耗体积和溶液pH的变化并将记录的滴定体积和pH绘制成pH-V图，根据所记录曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分的最大值对应的标准酸体积作为等当点，所绘制的图形如图2，图中一阶数值微分的得到滴定等当点体积为2.9035ml，相应的等当点为标准酸体积-pH变化图中所示的EP1，此等当点pH为5.02。等当点体积与浓度进行计算得到溶液的OH -浓度为0.0321mol/L。滴定从开始到结束约为10分钟。
从图2滴定曲线可明显看出，在滴定接近等当点前pH基本无变化，说明样品中Zn 2+与固体Zn(OH) 2ZnSO 4.xH 2O和溶液中的OH -构成缓冲体系，在这一阶段 是酸溶解样品中的Zn(OH) 2ZnSO 4.xH 2O，而pH基本无变化。接近等当点时，溶液中的氢氧化物耗尽，加入的酸使溶液pH剧烈下降，采用一阶数值微分对该曲线进行处理后，一阶数值微分曲线的最大值点即为滴定的等当点。
实施例3：此实施例为一段后液调酸后的碱化度测定，溶液成分为Zn 140g/L，Co 6mg/L，Ni 5mg/L，Ge 0.13mg/L，Cd 80mg/L，取热过滤液40ml，加水30ml，使用经标定的HCl溶液，实际浓度为0.1107mol/L作为滴定剂缓慢滴入测定样品，滴定至约pH3.8，记录标准酸消耗体积和溶液pH的变化并将记录的滴定体积和pH绘制成pH-V图，根据所记录曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分的最大值对应的标准酸体积即为等当点，所绘制的图形如下图3，图中一阶数值微分得到滴定等当点体积为0.4060ml，等当点pH为4.42。等当点体积与浓度进行计算得到溶液的OH -浓度为0.0045mol/L。滴定从开始到结束约为10分钟。
从上述3个不同溶液的实施例可以看出，滴定等当点的pH分别为4.27、5.02、4.42，充分说明的本发明人对滴定过程的分析，不同溶液的等当点pH不同，采用定pH滴定显然不能获得可靠的滴定终点，而采用本发明所述的方法解决了上述问题。
实施例4：此实施例为标定实验中使用的标准酸(即公知的方法对所配制的盐酸水溶液的H +浓度进行标定)，参考国标GB/T601-2003实施。本方法采用两次标定，第一次先标定标准碱的浓度，再使用标定的已知浓度的碱标准液用于标定所述的标准酸。碱液的标定的一个实施例为：将基准级邻苯二甲酸氢钾标准物质在105～110℃下烘干至恒重，将110g氢氧化钠溶于100ml无二氧化碳的水，置于密闭聚乙烯容器中放置至溶液清亮，取上层清亮溶液10.8ml，加水稀释至1000ml配制氢氧化钠滴定液。称取0.1377g经上述烘干至恒重的的邻苯二甲酸氢钾标准物质，加水至50～60ml，搅拌至完全溶解，使用同实施例1～3所述的终点判定原理由自动电位滴定仪滴定并绘图，所绘制图形见附图4，图中一阶数值微分的得到滴定等当点体积为3.3703ml，等当点pH为8.81，据此计算得氢氧化钠滴定液浓度为0.2001mol/l。滴定从开始至结束约5分钟。使用该经标准标定浓度的滴定液，对盐酸滴定液进行标定。将27ml盐酸加水稀释至1000ml，配制成盐酸滴定液。将3.0000ml该盐酸滴定液加入烧杯，加水至50～60ml，搅拌90秒后 使用同实施例1～3所述的终点判定原理由自动电位滴定仪滴定并绘图，所绘制图形见附图5。图中一阶数值微分得到滴定等当点体积为3.5589ml，等当点pH为7.45。以氢氧化钠滴定液浓度与盐酸加入体积计算，盐酸标准酸H +浓度为0.2374mol/l。滴定从开始至结束约5分钟。

Claims (9)

  1. 一种硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：取一定量的经热过滤的硫酸锌溶液，并加入适量的蒸馏水，插入pH电极在所述的硫酸锌样品溶液和水的混合物中；搅拌均匀后，采用已标定H +浓度的标准酸缓慢加入硫酸锌溶液中的OH -浓度，滴定过程不断搅拌；记录加入标准酸体积和pH的变化曲线，直至溶液pH小于3.5；并且滴定等当点采用标准酸加入体积和溶液pH的一阶微分曲线判断，采用等当点消耗的所述的标准酸计算溶液的OH -浓度。
  2. 根据权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述一定量热过滤溶液的体积是5～50ml，加入蒸馏水的量是50～100ml，所述的搅拌是采用磁力搅拌。
  3. 权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述标准酸为硫酸、盐酸，优选盐酸，纯度至少为分析纯。
  4. 权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述的标准酸浓度采用盐酸和蒸馏水配制，盐酸纯度至少为分析纯，所述的标准酸浓度以H +计的浓度为0.1～0.3mol/L，混匀后采用公知的方法对所配制的盐酸水溶液的H +浓度进行标定，标定浓度的盐酸水溶液即为所述的标准酸。
  5. 权利要求4所述的测定方法，其特征在于：采用所述标准酸缓慢加入滴定硫酸锌溶液中的OH -浓度的方法，所述的缓慢加酸是在10分钟内缓慢加入。
  6. 权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：记录加入标准酸体积V和溶液pH的变化并绘制pH-V曲线，根据所绘制的pH-V曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分曲线上ΔpH/ΔV的最大值对应的标准酸体积作为等当点；所述的记录加入标准酸体积和溶液pH是采用计算机控制的滴定仪自动记录，所述的一阶微分曲线也为计算机自动计算，滴定等当点也为所述的自动化滴定仪自动判断。
  7. 权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述热过滤是在温度70～90℃下进行，优选80～90℃。
  8. 如权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述滴定温度为室温。
  9. 如权利要求1所述的硫酸锌溶液中氢氧根浓度的测定方法，其特征在于：所述OH -浓度的测定方法为：取5～50ml在80～90度下热过滤的硫酸锌液，加 入50～100ml蒸馏水，采用0.1～0.3mol/l标定出浓度的盐酸，在搅拌下缓慢加入所述的已标定浓度的盐酸，直至溶液的pH小于3.5；记录滴定液消耗体积和溶液pH的变化并将记录的滴定体积-pH绘制成图形，根据所记录曲线计算并绘制ΔpH/ΔV-V一阶数值微分曲线，以所述的一阶数值微分曲线上ΔpH/ΔV-V的最大值对应的滴定液体积作为等当点；并且根据等当点所消耗的所述的标准酸消耗的体积计算试样的OH -浓度。
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