Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 7.5, app A
1. Introduction:
Metal Aluminum cannot react with nitric acid or concentrated sulfuric acid. It can dissolve in dilute sulfuric acid or hydrochloric acid. Active hydrogen, generated during the acid digestion process, will reduce arsenic to AsH3, which will escape from solution, resulting in a low or negative arsenic value. The proposed method sets up a protocol to dissolve metal alumina without loss of arsenic.
2. Reagent:
3M NaOH, 10% HgSO4 Solution, 30% H2O2
1:1 H2SO4, Concentrated HNO3, Tiling Copper.
3. Procedure:
3.1. Dissolve
3.1.1. Dissolve using NaOH (Method 1).
Weigh 0.5g of metal aluminum sample to a 125 ml Erlenmeyer flask, add 15 ml of 3M NaOH solution, allow to react and dissolve about 20 min. Again add 10ml of 3M NaOH, continue reaction until no gas bubbles are present and the sample is dissolved completely.
3.1.2. Dissolve using HgSO4 (Method 2)
Weigh 0.5g of metal Aluminum sample to a 125ml Erlenmeyer flask, add 10ml of 10% HgSO4 solution and 5ml of 30% H2O2. After 20 min., add appropriate amount of HgSO4. Allow reaction to continue until no gas bubbles are present. Add metal copper strips (large surface area) into the sample solution. After 10 min, withdraw the copper strips and add new copper strips. Repeat until the surface of copper strips in sample solution do not change to a silver color. Withdraw all copper strips from sample solution.
3.2. Digestion:
Add 3ml of concentrated HNO3, 5ml of 1:1 H2SO4 into the sample solution obtained from 3.1.1 or 3.1.2. Heat slowly and evaporate the sample solution until SO3 fumes are present for 5 min. Cool and dilute the sample to 50.0ml.
Determine As by Atomic Absorption method.
Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 7.5, app A