Industrial online pH meter and its application in mineral processing plants
Online detection of pH value of flotation slurry has always been a problem that plagues the mineral processing process. The key to using a pH meter well is reasonable selection, proper installation and careful maintenance. Shenzhen Pingao Testing also introduces to you the application of pH meters and specific technical measures in a certain mineral processing plant. This method is effective and has universal applicability to other similar flotation operations. The pH value of flotation slurry is very important in the mineral processing process. factors, related to the quality of mineral processing indicators. However, most mineral processing plants in my country have not implemented online detection of the pH value of the slurry. Online detection of the pH value of the slurry has always been a problem that plagues the automation of mineral processing in my country. Judging from the existing problems, the main manifestations are: short service life of electrodes, large errors, poor stability, and heavy maintenance. However, pH detection technology and products are relatively mature, and the measurement results are very good under laboratory conditions. However, the online detection of pH value in many mineral processing production processes is difficult to achieve satisfactory results, and even cannot be used normally. Some mineral processing plants have high requirements for pH value. Online testing can only be done at a distance, and some simply use pH test paper instead of a pH meter for measurement. The author believes that it is difficult to detect the pH value of slurry online. In addition to objective reasons, it is more due to the application party’s improper selection, maintenance and technical measures of the pH meter. To use a pH meter well in mineral processing, you must understand the principle, structure, selection, maintenance, etc. of a pH meter, and take reasonable measures based on the conditions on the mineral processing site.
Basic principles of pH measurement
Perhaps the most familiar and oldest zero-current measurement method used to determine the course of chemical reactions is pH measurement. Generally speaking, pH measurement is used to determine the acidity or alkalinity of a certain solution. Even chemically pure water is dissociated in trace amounts. The ionization equation is: H2O H2O=H3O-OH-(1) Since only a very small amount of water is dissociated, the molar concentration of ions is generally a negative power exponent. In order to avoid using the negative molar concentration Calculating power exponents, biologist Soernsen suggested in 1909 to replace this inconvenient value with a logarithm and define it as "pH value". Mathematically, pH is defined as the negative of the common logarithm of the hydrogen ion concentration. That is: pH=-log[H] (2) Since the ion product is highly dependent on temperature, for the pH value of process control, the temperature characteristics of the solution must be known at the same time. This can only be achieved when the measured medium is at the same temperature. Compare their pH values. In order to obtain and reproducible pH values, potentiometric analysis is used for pH measurements. The electrodes used in potentiometric analysis are called galvanic cells. The voltage of this battery is called electromotive force (EMF). This electromotive force (EMF) consists of 2 half cells. One half-cell is called the measuring electrode, and its potential is related to a specific ion activity; the other half-cell is the reference half-cell, usually called the reference electrode, which is generally connected to the measuring solution and connected to the measuring instrument. . The standard hydrogen electrode is the reference point for all potential measurements. The standard hydrogen electrode is a platinum wire that is electrolytically plated (coated) with platinum chloride and surrounded by hydrogen gas. The most familiar and commonly used pH indicating electrode is the glass electrode. It is a glass tube with a pH-sensitive glass membrane blown onto the end. The tube is filled with a KCI buffer solution containing saturated AgCI, with a pH value of 7. The potential difference that exists on both sides of the glass membrane reflects the pH value. This potential difference follows the Nernst formula: E=Eo. 1n[H3oq(3)n. 』In the formula: E - potential; E electrode standard voltage; R - gas constant; T - Kelvin temperature; F - Faraday constant; N - valence of the measured ion; [HO] - activity of HO ion. It can be seen from the above formula that the potential E has a certain relationship with the HO ion activity and temperature. At a certain temperature, measuring the potential E can calculate ln[HO] (convert to log[HO] to get pH), which is pH Basic principles of detection. In the Nernst formula, temperature "' plays a big role as a variable. As the temperature rises, the potential value will increase accordingly. For every 1°C increase in temperature, a 0.2mV/pH change in potential will occur. Expressed in terms of pH value, the pH value changes by 0.0033 per pH per I~C. This means that for measurements at 20~30~C and around 7pH, there is no need to compensate for temperature changes; while for temperatures greater than In applications where the temperature is 30°C or less than 20°C and the pH value is greater than 8 or less than 6, temperature changes must be compensated.
