Gravimetric analysis for different Au solutions重量分析方法计算电镀金用量1.0 Purpose1.1 The purpose of this document is to describe the gravimetric methods to analyze different Ausolutions including Acid Au bath, Aqua regia refining Au solution & Cyanide stripping Au refining solution etc. It’s not recommended to use gravimetric method if Au concentration is less than 0.5g/L.2.0 Associated Procedures & Materials2.1MSDS of H2SO4, HNO3, HCl, Na2SO3, PGC & Pd salt3.0Jig and Fixture Used3.1 N.A4.0 S afety Requirements4.1 Follow Area Safety Rules4.2Goggles4.3Safety shoes4.4Rubber Gloves & disposal plastic gloves4.5 Chemical Resistant Uniform,4.6 Chemical resistance apron5.0Equipment5.1Fume ‘ cupboard ‘5.225ml transfer pipette5.3Gooch Crucible5.4500ml Conical flask, 250ml, 500ml & 1 liter beaker with watch glass5.5High temperature furnace.(900 ºC)5.6Normal oven up to 250°5.7100ml measuring cylinder5.8Hot Plate(2~3kw)5.9Ashless filter paper5.10Funnel5.11Desiccator5.12Balance, accuracy is 0.0001gram6.0 R eagent6.1 Sulfuric acid (98%)6.2 Nitric acid (>65%)6.3 HCl concentrated & HCl(50v/v%);Address：16 Collyer Quay, #26-01 Income@Raffles, Singapore 049318 Tel:+ 65-6589 8045 Fax:+65- 6589 80416.4 Sodium sulfite, anhydrous, Na2SO36.5 Aqua regia (HNO3:HCl=1:3)7.0 C leanliness7.1 All beakers & volumetric flask used for analysis must be carefully cleaned with D.I. waterbefore being used.8. Procedure8.1. Procedure for citric acid Au bath & cyanide stripping refining solution8.1.0 Clean crucible with Aqua Regia & thoroughly wash with DI water,and then dry up in 110°C clean oven for 2 hrs. Store clean & driedcrucible in desiccator.8.1.1. Pipette 25ml sample(filtrate first if necessary) into a 500ml beaker8.1.2. Slowly add about 40ml Sulfuric acid (98%), and then cover withWatch glass8.1.3. Heat up the mixed solution until it becomes clear(but still in deepbrown color) on Heater, which will take 20~40min.The gold willform sponge.8.1.4. Cool down, slowly & carefully add DI water to dilute left Sulfu ricAcid;8.1.5. Use boiled hot DI water to wash sponge 2 times, and carefully pourout washing water to make sure no Au particle lost.8.1.6. Add concentrated Nitric Acid 20ml to boil sponge 10min., and thencool down.8.1.7. Use boiled hot DI water to wash for a few times.8.1.8 Transfer Au sponge & particles into weighted crucible(W1), and thendry for 2hrs@150°C in a clean oven;8.1.9. Switch off oven, and then cool down;8.1.10 Put crucible into disccator for 20min., and then weight crucibleAgain(W2)Calculation:Gold (g/L)=(W2-W1)x40Note:•Keep all washing solution & rinsing water in a big beaker, and mix well to verify Au concentration with AA machine after completion ofgravimetric analysis.•To minimize possible big analysis error, normally total Au attracted by gravimetric method should be more than 0.2g. Thus, the sampling volume can be more or less than 25ml.• A correlation in 900°C furnace >20min. show that there is no difference compared to 150°C oven dry 2hrs results.8.2. Procedure for gold refining aqua regia solution8.2.0 Prepare cleaned crucible same as 8.1.08.2.1 Pipette 25ml sample(filtrate first if necessary) into a 500ml beaker8.2.2 Add 10ml concentrated HCl, and then add DI water to about 150ml,mix well8.2.3Slowly add total 5grams Sodium Sulfite anhydrous, and m ix wellwith glass rod agitation;8.2.4Solution become turbid, which indicates Au ion is reducedAnd Au is precipitated.8.2.5Put on watch glass cover, and heat up on oven to just boiling, and thenswitch off hotplate to keep warm about 40min so as to Au particlescan completely settle down8.2.6Carefully pour out clear solution through ashless filter paper & funneland try the best not to pour out Au particles. The solution should becollected by 1 liter beaker8.2.7Use DI water(washing bottle) to wash watch glass & beaker& Auparticles, and keep for 20~40min. until Au particles completely settledown & water become clear.8.2.8Repeat 8.2.6 to carefully pour out clear solution.8.2.9Slowly add 30ml concentrated Sulfuric Acid into beaker, and put onthe hotplate to boil until white smoke coming out. Au particles willform sponge. This may take 20~40min.8.2.10C ool down beaker on asbestos mes h, and then carefully & slowly addDI water to dilute left solution, and then pour into 1 liter beakerthrough ashless filter paper.8.2.11W ash beaker, watch glass & sponge for a few times to neutral, andpour all of washing water through ashless filter paper.8.2.12T ransfer ashless paper & sponge to weighted crucible(W1), and putinto clean furnace & heat up to 150°C for 10~20min., and then uptemperature to 900°C for at least 30min.8.2.13S witch off furnace and cool down to about 100°C,and then take outthe crucible from the furnace to put into desiccator to store for halfhour;8.2.14W eight the dry crucible for (W2)Calculation:Gold (g/L)=(W2-W1)x40Note:•Keep all washing solution & rinsing water in a big beaker, and mix well to verify Au concentration with AA machine after completion ofgravimetric analysis.•To minimize possible big analysis error, normally total Au attracted by gravimetric method should be more than 0.2g. Thus, the sampling volume can be more or less than 25ml.。