Method for detecting concentration of hydrochloric acid in iron ion-containing pickling waste liquid

Abstract

The invention relates to a method for detecting the concentration of hydrochloric acid in an iron ion-containing pickling waste liquid, which comprises the following steps of: 1, adding NH4SCN and NaF into the iron ion-containing pickling waste liquid, and then adding an ethyl violet indicator to obtain a solution to be titrated; and 2, titrating the solution to be titrated by using a NaOH standard solution, when the color of the solution to be titrated is changed from blue to purple, judging that the titration end point is reflected, and recording the volume of the NaOH standard titration solution consumed by a sample. The ethyl violet is used as an indicator to measure the hydrochloric acid concentration of the pickling waste liquid, the titration error is within 0.2%, the method is more accurate compared with other common methods, and the hydrochloric acid measured concentration is closer to the original concentration.

Description

technical field [0001] The invention belongs to the technical field of detection, and relates to a method for detecting the concentration of hydrochloric acid in pickling waste liquid containing iron ions. Background technique [0002] In the manufacturing process of locomotive and vehicle parts, in order to increase the corrosion resistance of parts, they should be soaked with hydrochloric acid to remove rust, that is, pickling treatment. The concentration of hydrochloric acid in the pickling waste liquid not only affects the speed of pickling reaction, but also affects the next step. The addition amount of reaction raw materials and the length of reaction time in the process. The exothermic heat of the pickling reaction will also accelerate the volatilization of hydrochloric acid, and the hydrochloric acid dispersed in the air will corrode the equipment and cause harm to the body of the workshop operators. Therefore, in order to improve the treatment efficiency of picklin...

AI Technical Summary

Problems solved by technology

However, studies have shown that when there are iron ions in the hydrochloric acid solution at room temperature and the pH>2, Fe in the pickling waste liquid 3+ It will be the first to be hydrolyzed to form Fe(OH) 3 Precipitation, and this brick-red floc precipitation will directly interfere with the observation of the end point of the reaction of methyl orange from red to orange, resulting in a low concentration of hydrochloric acid

Therefore, most researchers will choose different masking agents to shield the influence of iron ions to reduce titration errors, but the commonly used acid-base indicators still cannot specify the reaction end point of the determination of the concentration of hydrochloric acid in some pickling waste liquids.

In this study, according to the method proposed by Qi Xiancheng et al., bromocresol green was used as an indicator to measure the concentration of hydrochloric acid in the pickling waste liquid, and it was found that the solution was yellow-green when pH>4, but because bromocresol green was only when pH>5 from yellow to blue-green, but at this time Fe 2+ Has begun to hydrolyze and precipitate, gray-green Fe(OH) 2 Precipitation will affect the end point indication of bromcresol green blue green

Experiments have shown that even with the use of masking agents to complex iron ions in pickling waste, the titration error is still large

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