Industrial pH meter and its application in concentrator
On-line detection of pH value of flotation pulp is always a difficult problem that puzzles the beneficiation process. The key to using pH meter well is reasonable selection, proper installation and careful maintenance. Shanghai Womao Instrument Technology Co., Ltd. introduces the application of industrial pH meter in a concentrator and the specific technical measures. This method has good effect and is universal for other similar flotation operations. The pH value of P flotation pulp is a very important factor in the beneficiation process, which is related to the quality of beneficiation indicators. However, most mineral processing plants in China have not realized on-line detection of pulp pH value, and on-line detection of pulp pH value has always been a difficult problem that puzzles China's mineral processing automation. Judging from the existing problems, the main manifestations are: short service life, large error, poor stability, large maintenance and so on. However, the pH detection technology and products are relatively mature, and the measurement effect is very good under laboratory conditions. However, the online detection of pH value in many mineral processing processes is difficult to achieve satisfactory results, or even can not be used normally. Some mineral processing plants can only stay away from online detection of pH value, and some simply use pH test paper instead of pH meter to measure. In the author's opinion, it is difficult to detect the pH value of pulp online. Apart from objective reasons, it is more due to the improper selection, maintenance and technical measures of the pH meter by the application side. In order to make good use of pH meter in mineral processing, it is necessary to understand the principle, structure, selection and maintenance of pH meter, and take reasonable measures according to the situation of mineral processing site.
1 The basic principle of pH measurement
I am afraid that the old zero-current measurement method used to determine the chemical reaction process is pH measurement. Generally speaking, pH measurement is used to determine the pH of a solution. Even a small amount of chemically pure water is dissociated, and its ionization equation is: H2O H2O=H3O-OH-(1) Because only a small amount of water is dissociated, the molar concentration of ions is generally a negative power exponent. In order to avoid using the negative power exponent of molar concentration for operation, biologist Soernsen suggested in 1909 to replace this inconvenient value with logarithm and define it as "pH value". Mathematically, the pH value is defined as the negative value of the common logarithm of hydrogen ion concentration. That is, pH= a log[H ](2) Because the ionic product is very dependent on temperature, the temperature characteristics of the solution must be known at the same time for the pH value of process control, and the pH values can only be compared when the measured medium is at the same temperature. In order to obtain * * and reproducible pH value, it is necessary to use potentiometry to measure pH value. The electrode used in potentiometric analysis is called a galvanic cell. The voltage of this battery is called electromotive force (EMF). This electromotive force (EMF) consists of two half cells. One half cell is called a measuring electrode, and its potential is related to specific ion activity. The other half cell is a reference half cell, usually called a reference electrode, which is generally communicated with the measuring solution and connected with the industrial pH meter. The standard hydrogen electrode is the reference point for all potential measurements. The standard hydrogen electrode is a platinum wire, which is plated (coated) with platinum chloride by electrolysis and filled with hydrogen around it. * Familiar with * The commonly used pH indicator electrode is a glass electrode. It is a glass tube with a pH-sensitive glass film blown on the end. The tube is filled with KCI buffer solution containing saturated AgCI, and its pH value is 7. The potential difference that exists on both sides of the glass film and reflects the pH value follows Nernst formula: E = EO.1n [H3OQ (3) n. Where: e-potential; Standard voltage of e electrode; R-gas constant; T-Kelvin * * temperature; F-Faraday constant; N-valence of the ion to be measured; Activity of [HO]-HO ion. From the above formula, it can be seen that the potential E has a certain relationship with the activity and temperature of HO ions. At a certain temperature, ln[HO] can be calculated by measuring the potential E (converted into a log[HO] to obtain pH), which is the basic principle of pH detection. In Nernst formula, temperature plays an important role as a variable. As the temperature rises, the potential value will increase. As the temperature increases every 1℃, the potential will change by 0.2 mv/pH.. Expressed by pH value, the ph value changes by 0.0033pH per I~C per lpH. That is to say, for the measurement of 20 ~ 30℃ and 7pH, there is no need to compensate for the temperature change; However, for applications where the temperature is greater than 30℃ or less than 20℃ and the pH value is greater than 8 or less than 6, the temperature change must be compensated.
