test method for content of liquid polymerized ferric sulfate

The detection methods of liquid Polyferric Sulfate content are summarized, which are divided into three categories: core index detection (total iron content and salt base degree) and auxiliary methods based on national standards and commonly used industry technologies:

I. Total iron content detection (core index)

1.Potassium dichromate titration method (national standard arbitration method)

1.Principle: In an acidic environment, tin chloride is used to reduce Fe³⁺ to Fe²⁺, and excess tin chloride is eliminated by mercury chloride, and then potassium dichromate is titrated to the purple endpoint.

2.step ：

3.① Take 1.5g sample + 20ml water + 20ml hydrochloric acid (1:1) → boil for 1 minute;

4.② Add a solution of stannous chloride to the yellow color disappears → cool quickly;

5.③ Add 5ml saturated mercury chloride solution → stand for 1 minute;

6.④ Add 50ml water + 10ml sulfur phosphorus mixed acid + 4~5 drops of sodium dianilatesulfonic acid → titrate with potassium dichromate until purple (30 seconds does not fade).

7.Calculation: total iron content (%) = (V × C × 05585 × 100) / m

8.(V: titration volume, C: potassium dichromate concentration, m: sample mass)

9.Note: Mercury chloride is toxic and waste liquid should be disposed of in accordance with regulations.

2.Atomic absorption spectroscopy (AAS)

1.Principle: After the sample is dissolved, iron atoms absorb characteristic wavelength light and are quantified by absorbance.

2.step ：

3.① The sample is dissolved in dilute acid (e.g., hydrochloric acid) → filter and dilute;

4.② Standard curve method for determination of absorbance.

5.Advantages: high precision (±1%), can measure a variety of metals at the same time.

3.Potassium permanganate titration method (reducing substance detection)

1.Application: Fe²⁺ content detection (affect the accuracy of total iron).

2.Step: Sample + sulfuric acid/phosphoric acid → titrate with 0.01mol/L potassium permanganate to the reddish endpoint.

Ⅱ. Salt base detection (key auxiliary indicators)

Principle: Hydrochloric acid depolymerizes the sample, potassium fluoride masks the iron ion, and sodium hydroxide titrates the free acid.

National standard steps (GB/T14591-2016):

1.Take 1.2~1.3g sample + 25ml hydrochloric acid standard solution → leave at room temperature for 10 minutes;

2.Add 10ml potassium fluoride solution (mask Fe³⁺) → Add 5 drops phenolphthalein;

3.Titrate with sodium hydroxide to a pale red color (30 seconds without fading).

4.Calculation: Base degree (%) = [(V0-V) × C × 017 × 100] / (m × iron content%)

5.(V0/V: blank/sample titration volume, C: NaOH concentration)

III. Quick-aid methods

1.Density association method

3.Application scenario: rapid estimation on production site.

4.operate ：

5.① Constant temperature (20±1℃) measure the sample into the densitometer;

6.② When the density is greater than or equal to 1.45g/cm³, the total iron content is about 11.5%; if it is less than 1.3g/cm³, it is unqualified.

7.Limitations: It needs to be calibrated with titration.

2.pH detection

8.Standard: The pH of 1% aqueous solution should be 2~3 (National standard GB/T14591-2016).

IV. Notes

1.Reagent calibration: The titrant (such as potassium dichromate, sodium hydroxide) should be calibrated in advance.

2.Interference elimination:

9.When the base degree is more than 16%, iron hydroxide precipitates are easy to be formed, so acid control should be strict;

10.Arsenic, lead and other heavy metals are detected by atomic absorption spectrometry.

3.safe operation ：

11.The boiling step of hydrochloric acid should be done in a fume hood;

12.Mercury chloride is a highly toxic substance, and it is recommended to use mercury-free methods (such as titanium trichloride method).

 propose

● Accuracy priority: select potassium dichromate method (total iron) or AAS method (in line with ISO standard);

● Rapid screening: combination of density method and pH method;

● Comprehensive quality control: simultaneous detection of salinity (8%~16% is optimal) and heavy metals.