Boron (B): Boron is generally found in seawater, and its content can reach 5mg / L. The content is lower in inland saline lakes. Boron is not a source of pollution, but due to its adverse effects in certain environments, it must be removed in the electronics industry. The chemical properties of boron are similar to those of silicon.When the pH is higher than 10, it exists as a monovalent borate anion, and when the pH is lower than 10, it exists as non-ionized boric acid B (OH) 3 The salt removal rate is related to the pH value. When the pH value is high, the removal rate is also high.
Silica (SiO2): Silica is an anion in some cases. Its chemical properties are complex and even unpredictable. TOC (in terms of carbon) represents the total amount of organic matter without specifying the composition of the organic matter. Similarly, the silicon concentration only indicates the total concentration of silicon, but does not specify the concentration of various constituents of silicon. The total amount of silicon in the water includes active silicon and colloidal silicon. Active silicon is soluble silicon, which is weakly ionized and does not polymerize into long chains. Active silicon is the desired form in RO and ion exchange processes, and it is also the form of silica used in IMSDesign software. Although the active silica has anionic properties, it is not included in the anion-cation balance in the anion mode in the water analysis, but is included in the TDS in the form of salt. Colloidal silicon is polymeric or colloidal, and is closer to a solid in terms of its properties. Colloidal silicon can be removed by the RO system, but may cause colloidal contamination at the front end of the RO. The diameter of colloidal silicon can be as small as 0.008 microns, but only parts larger than or equal to 0.45 microns can be measured by SDI. Clay, silt, sand and other particulate silicon mixtures generally have a diameter of 1 micron or larger, which can be measured with an SDI instrument. Under the condition of using silicon dispersant, the solubility limit of active silicon is 100-150%. Increasing temperature and pH value below 7.0 or above 7.8 will increase the solubility of silicon. When the presence of iron ions that catalyze the polymerization of silicon, the solubility of active silicon decreases. In the RO system, the removal rate of silicon is closely related to the pH value of the raw water. As the pH value increases, the removal rate also increases. This is because the active silicon is more in the form of a salt than an acid. .
Carbon dioxide (CO2): Carbon dioxide is a gas that reacts with water to form weak carbonic acid (H2CO3) when dissolved in water. If carbon dioxide is in a saturated state in pure water, its concentration is about 1600 mg / L and its pH is about 4.0. The source of carbon dioxide in natural water bodies is based on the bicarbonate balance of pH. The concentration of carbon dioxide in water is indirectly determined by the corresponding relationship between pH and bicarbonate concentration. Carbon dioxide and bicarbonate ions maintain equilibrium in the pH range of 4.4-8.2. Both carbon dioxide was at pH 4.4 and bicarbonate at pH 8.2. The IMSDesign program uses bicarbonate concentration and pH value to calculate carbon dioxide concentration in water. Because carbon dioxide is a gas, the RO membrane has no removal or concentration effect on it, and its concentration is the same in feed water, produced water and concentrated water. Adding acid to the feedwater will bicarbonate to carbon dioxide, so the pH value will drop.
Hydrogen sulfide (H2S): Hydrogen sulfide is in a gaseous state, which makes the feedwater smell of rotten eggs. Its 0.1mg / L concentration is the critical value of odor. At a concentration of 3-5mg / L, it has a strong odor. Hydrogen sulfide is easily oxidized into sulfur by oxidants such as air, chlorine and potassium permanganate. The effect of sulfur is similar to colloidal pollution, which cannot be removed with traditional media filters. In the system design, it is recommended to keep the hydrogen sulfide in a gaseous state and pass it through the RO system to produce water, and then treat and remove the produced water.
