EDTA容量法測(cè)定鉛.doc

EDTA容量法測(cè)定鉛1方法提要試樣用酸分解，在酸性介質(zhì)中，鉛離子與硫酸根作用生成硫酸鉛沉淀，與鐵、銅、鋅、鎘等元素分離。再在PH56的醋酸-醋酸鈉緩沖溶液中，將硫酸鉛轉(zhuǎn)化成醋酸鉛。以二甲酚橙或半二甲酚橙為指示劑，用EDTA標(biāo)準(zhǔn)溶液滴定。銻、鉍含量較高時(shí)，易水解并夾雜于硫酸鉛沉淀中，可加入酒石酸絡(luò)合以消除其干擾，鋇大于10mg時(shí)，由于生成PbSO4BaSO4復(fù)鹽沉淀，使鉛的結(jié)果偏低。本法適用一般礦石（Pb）/10-25的測(cè)定。2試劑21.鹽酸（p1.19g/mL），分析純。22.硫酸（p1. 84g/mL），分析純。23.硝酸（p1.42g/mL），分析純。24.高氯酸（p1.68g/mL），分析純。25.冰醋酸（p1.05g/mL），分析純。26.二甲酚橙或半二甲酚橙指示劑：稱(chēng)取0.5g二甲酚橙或半二甲酚橙溶于100mL水中。 27.酒石酸溶液：稱(chēng)取20g酒石酸溶于100mL水中。28.醋酸-醋酸鈉緩沖溶液（PH56）：稱(chēng)取200gCH3COONa3H2O溶于水中，加10mL冰醋酸，用水稀釋至1000mL，搖勻。29.將金屬鉛（99.99%）于硝酸（10+90）中浸泡1min，取出，用乙醇洗凈，于50烘干。210.鉛標(biāo)準(zhǔn)溶液的配制：準(zhǔn)確稱(chēng)取4.1442g或2.0721g于50烘干的金屬鉛（99.99%）于250mL燒杯中，加入20mLHNO3(1+1)，低溫加熱使其溶解，冷卻后移入1000mL容量瓶中，用水稀釋至刻度，混勻。此液為C（Pb）=0.02000mol/L或C（Pb）=0.01000 mol/L。211.EDTA標(biāo)準(zhǔn)溶液的配制：分別稱(chēng)取120g或60gEDTA于1000mL水中，加熱溶解，用水稀釋至16L，混勻，放置過(guò)夜，此溶液為C（EDTA）=0.02000 mol/L或C（EDTA）=0.01000mol/L。212.EDTA標(biāo)準(zhǔn)溶液的標(biāo)定：準(zhǔn)確分取鉛標(biāo)準(zhǔn)溶液30.00ml于250ml燒杯中，用水稀釋至100ml左右，加入1滴對(duì)硝基酚指示劑，用氨水（1+1）調(diào)至黃色，再用鹽酸（1+3）調(diào)至恰好無(wú)色，加入2530mL醋酸-醋酸鈉緩沖溶液（PH56），二甲酚橙或半二甲酚橙指示劑2滴，以欲標(biāo)定的EDTA滴至亮黃色即為終點(diǎn)。若消耗EDTA溶液不等于30.00mL，則運(yùn)用稀釋定律調(diào)整至消耗體積為30.00mL，并作平行標(biāo)定予以確認(rèn)。3分析步驟稱(chēng)取0.2000g（視含量而定）在105烘2h的試樣于250mL燒杯中，用少量水潤(rùn)濕，加入15mL氯酸鉀硝酸保和液，蓋上表面皿，置于電爐上加熱溶解56min至樣品完全分解（無(wú)黑色殘?jiān)?，?0mL濃硫酸，加熱至冒濃厚三氧化硫白煙，取下冷卻，用水沖洗表面皿及杯壁后，置于電爐上加熱至冒三氧化硫白煙，取下冷卻。加50mL水（若銻、鉍含量較高時(shí)，加5mL酒石酸溶液），加熱煮沸510min使可溶性鹽類(lèi)溶解，取下放置4h以上。以慢速定量濾紙過(guò)濾，用硫酸（5+95）洗至無(wú)鐵離子。將沉淀及濾紙放回原燒杯中，加入30mL醋酸-醋酸鈉緩沖溶液（PH56）和25mL水加熱煮沸約10min，使硫酸鉛溶解，用水稀釋至100mL，加0.1g抗壞血酸，攪拌1min，加3滴二甲酚橙或半二甲酚橙指示劑，用相應(yīng)的EDTA標(biāo)準(zhǔn)溶液滴定至顏色由紫紅色變?yōu)榱咙S色即為終點(diǎn)。隨同試樣做空白試驗(yàn)。4分析結(jié)果的計(jì)算按下式計(jì)算鉛的含量：（Pb）/10-2= C（VV0）M/10m式中：CEDTA標(biāo)準(zhǔn)溶液的濃度，mol/L；V0滴定空白時(shí)消耗EDTA標(biāo)準(zhǔn)溶液的體積，mL；V滴定試樣時(shí)消耗EDTA標(biāo)準(zhǔn)溶液的體積，mL；M鉛的摩爾質(zhì)量；m稱(chēng)取試樣的質(zhì)量，g。5允許誤差鐵礦中鉛的結(jié)果的差值應(yīng)滿足表3的誤差要求。有色金屬礦石、硫鐵礦或自然硫、螢石、選礦樣品中鉛的結(jié)果的差值應(yīng)滿足表3的誤差要求。鉛精礦應(yīng)滿足表8的要求。表8（GB）X(%)差值(%)X(%)差值(%)X(%)差值(%)X(%)差值(%)35.000.3248.000.3661.000.3974.000.4336.000.3249.000.3662.000.3975.000.4337.000.3250.000.3663.000.4076.000.4338.000.3351.000.3664.000.4077.000.4439.000.3352.000.3765.000.4078.000.4440.000.3353.000.3766.000.4179.000.4441.000.3454.000.3767.000.4180.000.4542.000.3455.000.3868.000.4181.000.4543.000.3456.000.3869.000.4182.000.4544.000.3457.000.3870.000.4283.000.4545.000.3558.000.3871.000.4284.000.4646.000.3559.000.3972.000.4285.000.4647.000.3560.000.3973.000.4386.000.46EDTA volumetric method for the determination of lead1. Summary of the methodAcid decomposition of the sample, in acidic media, lead sulfate generated and lead sulfate precipitate, and separation of elements such as iron, copper, zinc and cadmium. Then in the PH56 in acetic acid-sodium acetate buffer solution, lead sulfate into lead acetate. With xylenol orange or semi-xylenol orange as indicator, titration with EDTA standard solution. Antimony and bismuth high, easily hydrolyze and inclusion in lead sulphate in precipitation, may join tartrate complex to eliminate their interference, barium is greater than the 10mg, due to generate PbSO4 BaSO4 compound salt precipitation, low lead results.This method applies the General ore (Pb) determination of the/10-25.2. Reagents21. hydrochloric acid (p1.19g/mL), analysis of pure.22. sulfate (P1. 84g/mL), analysis of pure.23. nitric acid (p1.42g/mL), analysis of pure.24. perchloric acid (p1.68g/mL), analysis of pure.25. glacial acetic acid (p1.05g/mL), analysis of pure.26. xylenol orange or semi-xylenol Orange indicator: taking 0.5G xylenol orange or semi-xylenol Orange dissolves in 100mL in the water.27. tartaric acid solution: call of 20G tartaric acid dissolves in 100mL water.28. acetic acid-sodium acetate buffer solution (PH56): take 200gCH3COONa 3H2O in soluble in water, and 10mL acetic acid, diluted with water to 1000mL, shake.29. the metal lead (99.99%) in nitric acid (10+90) 1min immersed in, out, washed with ethanol, at 50 c drying.210. preparation of standard solutions of lead: accurate says take 4.1442g or 2.0721g to 50 and drying of metallic lead (99.99%) in 250mL the beaker, add 20mLHNO3 (1+1), low temperature heating makes it dissolved, moved into a 1000mL volumetric flask after cooling, dilute with water to scale, mix. This liquid is c (Pb) =0.02000mol/L, or c (Pb) =0.01000 mol/L.2 11.EDTA preparation of standard solution: get 120g or 60gEDTA respectively in 1000mL water, heated to dissolve, dilute with water to 16L, blended, place for the night, this solution is c (EDTA) =0.02000 mol/L, or c (EDTA) =0.01000mol/L.2 12.EDTA standard solution of calibration: accurate min take lead standard solution 30.00ml Yu 250ml beaker in the, water dilution to 100ml around, joined 1 drops on Nitro phenol indicates agent, with ammonia (1+1) adjusting to yellow, then with hydrochloride (1+3) adjusting to just colorless, joined 2530mL acetate-acetate sodium buffer solution (PH56), second cresol orange or half second cresol Orange indicates Agent 2 drops, to to calibration of EDTA drops to light yellow is for end.If consumption of EDTA solution is not equal to 30.00mL, the adjustment to consumption volume using dilution law is 30.00mL, and be recognized for parallel calibration.3. The analysis stepSaid take 0.2000g (depending on content and will) in 105 baking 2H of sample Yu 250mL beaker in the, with small water wetting, joined 15mL hydrochloride, cover Shang surface dish, placed furnace Shang heating dissolved 56min Hou, joined 5mL nitric acid and 1mL perchlorate, continues to heating to samples full decomposition (no black residue), plus 20mL sulfate (1+1), heating to risk strong three oxidation sulfur white smoke, removed cooling, water washing surface dish and the cup wall Hou, placed furnace Shang heating to risk three oxidation sulfur white smoke, removed cooling. Add a 50mL water (antimony, bismuth is high, increase 5mL tartrate solution), soluble salts dissolved in boiling heat 510min, remove the place 4H. Quantitative filter paper filter at slow speed, sulfate (5+95) to wash without iron ion. Will precipitation and the filter paper placed back original beaker in the, joined 30mL acetate-acetate sodium buffer solution (PH56) and 25mL water heating boiled about 10min, makes sulfate lead dissolved, water dilution to 100mL, plus 0.1g Ascorbic acid, mixing 1min, plus 3 drops second cresol orange or half second cresol Orange indicates agent, with corresponding of EDTA standard solution titration to color by purple red becomes light yellow is for end. Along with the blank test specimens.4. Analysis of results of calculationLead content based on the following:（Pb）/10-2= C（VV0）M/10mIn the formula: c-EDTA concentrations of standard solution, mol/L;V0-standard solutions of EDTA titration blank consumption volume, in mL;V-consumption standard solutions of EDTA titration sample volume, mL;Molar mass of the m-lead;M-take the quality of the sample, g.5. Permissible errorDifference of lead in iron ore results errors in table 3 requirements should be met. Non-ferrous metal ores,