EDTA容量法测定铅.doc

EDTA容量法测定铅
1．方法提要
试样用酸分解，在酸性介质中，铅离子与硫酸根作用生成硫酸铅沉淀，与铁、铜、锌、镉等元素分离。再在PH5～6的醋酸-醋酸钠缓冲溶液中，将硫酸铅转化成醋酸铅。以二甲酚橙或半二甲酚橙为指示剂，用EDTA标准溶液滴定。锑、铋含量较高时，易水解并夹杂于硫酸铅沉淀中，可加入酒石酸络合以消除其干扰，钡大于10mg时，由于生成PbSO4·BaSO4复盐沉淀，使铅的结果偏低。
本法适用一般矿石ω（Pb）/10-2＞5的测定。
2．试剂
2·1.盐酸（p1.19g/mL），分析纯。
2·2.硫酸（p1. 84g/mL），分析纯。
2·3.硝酸（p1.42g/mL），分析纯。
2·4.高氯酸（p1.68g/mL），分析纯。
2·5.冰醋酸（p1.05g/mL），分析纯。
2·6.二甲酚橙或半二甲酚橙指示剂：称取0.5g二甲酚橙或半二甲酚橙溶于100mL水中。
2·7.酒石酸溶液：称取20g酒石酸溶于100mL水中。
2·8.醋酸-醋酸钠缓冲溶液（PH5～6）：称取200gCH3COONa·3H2O溶于水中，加10mL冰醋酸，用水稀释至1000mL，摇匀。
2·9.将金属铅（99.99%）于硝酸（10+90）中浸泡1min，取出，用乙醇洗净，于50℃烘干。
2·10.铅标准溶液的配制：准确称取4.1442g或2.0721g于50℃烘干的金属铅（99.99%）于250mL烧杯中，加入20mLHNO3(1+1)，低温加热使其溶解，冷却后移入1000mL容量瓶中，用水稀释至刻度，混匀。此液为C（Pb）=0.02000mol/L或C（Pb）=0.01000 mol/L。
2·11.EDTA标准溶液的配制：分别称取120g或60gEDTA于1000mL水中，加热溶解，用水稀释至16L，混匀，放置过夜，此溶液为C（EDTA）=0.02000 mol/L或C（EDTA）=0.01000mol/L。
2·12.EDTA标准溶液的标定：准确分取铅标准溶液30.00ml于250ml烧杯中，用水稀释至100ml左右，加入1滴对硝基酚指示剂，用氨水（1+1）调至黄色，再用盐酸（1+3）调至恰好无色，加入25～30mL醋酸-醋酸钠缓冲溶液（PH5～6），二甲酚橙或半二甲酚橙指示剂2滴，以欲标定的EDTA滴至亮黄色即为终点。
若消耗EDTA溶液不等于30.00mL，则运用稀释定律调整至消耗体积为30.00mL，并作平行标定予以确认。
3．分析步骤
称取0.2000g（视含量而定）在105℃烘2h的试样于250mL烧杯中，用少量水润湿，加入15mL氯酸钾硝酸保和液，盖上表面皿，置于电炉上加热溶解5～6min至样品完全分解（无黑色残渣），加10mL浓硫酸，加热至冒浓厚三氧化硫白烟，取下冷却，用水冲洗表面皿及杯壁后，置于电炉上加热至冒三氧化硫白烟，取下冷却。加50mL水（若锑、铋含量较高时，加5mL酒石酸溶液），加热煮沸5～10min使可溶性盐类溶解，取下放置4h以上。以慢速定量滤纸过滤，用硫酸（5+95）洗至无铁离子。将沉淀及滤纸放回原烧杯中，加入30mL醋酸-醋酸钠缓冲溶液（PH5～6）和25mL水加热煮沸约10min，使硫酸铅溶解，用水稀释至100mL，加0.1g抗坏血酸，搅拌1min，加3滴二甲酚橙或半二甲酚橙指示剂，用相应的EDTA标准溶液滴定至颜色由紫红色变为亮黄色即为终点。随同试样做空白试验。
4．分析结果的计算
按下式计算铅的含量：
ω（Pb）/10-2= C（V－V0）M/10m
式中：C─EDTA标准溶液的浓度，mol/L；
V0—滴定空白时消耗EDTA标准溶液的体积，mL；
V─滴定试样时消耗EDTA标准溶液的体积，mL；
M─铅的摩尔质量；
m─称取试样的质量，g。
5．允许误差
铁矿中铅的结果的差值应满足表3的误差要求。有色金属矿石、硫铁矿或自然硫、萤石、选矿样品中铅的结果的差值应满足表3的误差要求。铅精矿应满足表8的要求。
表8（GB）
X(%)
差值(%)
X(%)
差值(%)
X(%)
差值(%)
X(%)
差值(%)
35.00
0.32
48.00
0.36
61.00
0.39
74.00
0.43
36.00
0.32
49.00
0.36
62.00
0.39
75.00
0.43
37.00
0.32
50.00
0.36
63.00
0.40
76.00
0.43
38.00
0.33
51.00
0.36
64.00
0.40
77.00
0.44
39.00
0.33
52.00
0.37
65.00
0.40
78.00
0.44
40.00
0.33
53.00
0.37
66.00
0.41
79.00
0.44
41.00
0.34
54.00
0.37
67.00
0.41
80.00
0.45
42.00
0.34
55.00
0.38
68.00
0.41
81.00
0.45
43.00
0.34
56.00
0.38
69.00
0.41
82.00
0.45
44.00
0.34
57.00
0.38
70.00
0.42
83.00
0.45
45.00
0.35
58.00
0.38
71.00
0.42
84.00
0.46
46.00
0.35
59.00
0.39
72.00
0.42
85.00
0.46
47.00
0.35
60.00
0.39
73.00
0.43
86.00
0.46

EDTA volumetric method for the determination of lead
1. Summary of the method
Acid 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 PH5~6 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 ω (Pb) determination of the/10-2>5.
2. Reagents
2·1. hydrochloric acid (p1.19g/mL), analysis of pure.
2·2. sulfate (P1. 84g/mL), analysis of pure.
2·3. nitric acid (p1.42g/mL), analysis of pure.
2·4. perchloric acid (p1.68g/mL), analysis of pure.
2·5. glacial acetic acid (p1.05g/mL), analysis of pure.
2·6. xylenol orange or semi-xylenol Orange indicator: taking 0.5G xylenol orange or semi-xylenol Orange dissolves in 100mL in the water.
2·7. tartaric acid solution: call of 20G tartaric acid dissolves in 100mL water.
2·8. acetic acid-sodium acetate buffer solution (PH5~6): take 200gCH3COONa · 3H2O in soluble in water, and 10mL acetic acid, diluted with water to 1000mL, shake.
2·9. the metal lead (99.99%) in nitric acid (10+90) 1min immersed in, out, washed with ethanol, at 50 ° c drying.
2·10. 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 25~30mL acetate-acetate sodium buffer solution (PH5~6), 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 step
Said 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 5~6min 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 5~10min, 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 (PH5~6) 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 calculation
Lead content based on the following:
ω（Pb）/10-2= C（V－V0）M/10m
In 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 error
Difference of lead in iron ore results errors in table 3 requirements should be met. Non-ferrous metal ores, pyrites or of lead in sulfur, and beneficiation of fluorite samples resulting difference error of table 3 requirements should be met. Lead concentrate shall meet the requirements of table 8.
Table 8 (GB)
X(%)
difference (%)
X(%)
difference (%)
X(%)
difference (%)
X(%)
difference (%)
35.00
0.32
48.00
0.36
61.00
0.39
74.00
0.43
36.00
0.32
49.00
0.36
62.00
0.39
75.00
0.43
37.00
0.32
50.00
0.36
63.00
0.40
76.00
0.43
38.00
0.33
51.00
0.36
64.00
0.40
77.00
0.44
39.00
0.33
52.00
0.37
65.00
0.40
78.00
0.44
40.00
0.33
53.00
0.37
66.00
0.41
79.00
0.44
41.00
0.34
54.00
0.37
67.00
0.41
80.00
0.45
42.00
0.34
55.00
0.38
68.00
0.41
81.00
0.45
43.00
0.34
56.00
0.38
69.00
0.41
82.00
0.45
44.00
0.34
57.00
0.38
70.00
0.42
83.00
0.45
45.00
0.35
58.00
0.38
71.00
0.42
84.00
0.46
46.00
0.35
59.00
0.39
72.00
0.42
85.00
0.46
47.00
0.35
60.00
0.39
73.00
0.43
86.00
0.46