微波消解-磺基水杨酸光度法测定磷矿石中铁

Determination of iron in phosphate ore by sulfosalicylic acid spectrophotometry with microwave digestion

磺基水杨酸光度法测定铁是比较经典的方法,但对于磷矿石,采用敞口聚四氟乙烯烧杯在电热板上溶矿过程中溶液易喷溅,且显色时在pH 8~11溶液中,PO_4^(3-)会跟磷矿石中的Ca^(2+)、Mg^(2+)反应生成沉淀而影响铁的测定,同时含锰高的磷矿石中的Mn^(2+)也会对铁的测定产生干扰。因此实验在HNO_3-HF-SSA(磺基水杨酸)混合酸里采用密闭高压微波消解技术快速消解各种磷矿石,并通过磺基水杨酸光度法在六次甲基四胺介质中测定磷矿石中铁(以Fe_2O_3形式表示)。考察确定了微波消解条件(功率400 W、压力0.5 MPa、消解时间10min)和混合酸的最佳用量(2mL HNO_3-5mL HF-2mL 200g/L SSA溶液),并对磷矿石国家标准物质和实际样品分析,结果表明,实验方法与国家标准方法(GB/T 1871.2—1995)以及电感耦合等离子体原子发射光谱法(ICP-AES)测定结果一致,测定值与认定值一致,相对标准偏差(RSD,n=5)在2%以内,可满足磷矿石中0.05%~10%三氧化二铁的测定要求。

Sulfosalicylic acid spectrophotometry is a classical method for the determination of iron.For phosphate ore,however,the solution is easily spattered in sample dissolution process in open PTFE beaker on electric hot plate.Moreover,PO43-can react with Ca2＋and Mg2＋in phosphate ore to form precipitates during coloring at pH 8-11,which influences on the determination of iron.The Mn2＋in phosphate ore containing high content manganese also has interference.The phosphate ore samples were rapidly dissolved in closed high-pressure microwave digestion system using HNO3-HF-SSA（sulfosalicylic acid）mixture.The content of iron（in Fe2O3）in phosphate ore was determined in hexamethylenetetramine medium by sulfosalicylic acid spectrophotometry.The microwave digestion conditions were obtained as below：the power was 400 W,the pressure was 0.5MPa,and the digestion time was 10 min.The optimized dosage of acid mixture was 2mL HNO3-5mL HF-2mL 200g/L SSA solution.The certified reference material and actual sample of phosphate ore were analyzed according to the experimental method.The found results were consistent with those obtained by national standard method（GB/T 1871.2-1995）and inductively coupled plasma atomic emission spectrometry（ICP-AES）as well as certified values.The relative standard deviations（RSD,n=5）were less than 2%,which could meet the determination requirements of Fe2O3（0.05%-10%）in phosphate ore.