Coating knowledge: how to improve the whiteness of titanium dioxide

Core tip: for pigment titanium dioxide, in addition to taking some measures to improve the whiteness in production, the key lies in the removal of impurities Impurities have a great negative impact on whiteness The more thoroughly impurities are removed, the higher the whiteness of the product, which means more to be used in coatings In the production process of titanium dioxide, if the impurities are not completely removed, when calcined at high temperature, many impurity elements such as iron, manganese, vanadium, lead, chromium, cobalt, cerium, copper, cadmium, nickel, molybdenum, etc exist in the oxide state, and these colored oxides show various hues, which affects the hues of the whole titanium dioxide Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Paint Home News: for pigment titanium dioxide, in addition to taking some measures to improve the whiteness in production, the key lies in the removal of impurities Impurities have a great negative impact on whiteness The more thoroughly impurities are removed, the higher the whiteness of the product, which is of greater significance in the paint In the production process of titanium dioxide, if the impurities are not completely removed, when calcined at high temperature, many impurity elements such as iron, manganese, vanadium, lead, chromium, cobalt, cerium, copper, cadmium, nickel, molybdenum, etc exist in the oxide state, and these colored oxides show various hues, so that the color of the whole titanium dioxide is affected but not pure white, which greatly affects the quality of the product Therefore, a variety of methods must be used to remove impurities 1 to remove impurities in mineral processing, first of all, mineral processing is necessary Because any ilmenite is usually mixed with many gangues and other minerals of paragenesis, accompaniment and recombination Mineral processing is to separate Ilmenite from them by using different physical and chemical properties of minerals and various effective methods For example, for gravity beneficiation of shaking table, most gangues in cast iron ore can be removed, and then magnetic separation can be carried out by magnetic separator to let the minerals pass through the magnetic field Because ilmenite is a paramagnetic mineral with high permeability, which can be attracted by magnet but can not attract iron itself, magnetized and demagnetized, but can be attracted by disk Other non ilmenite with low permeability cannot be attracted by disk and separated In the production of titanium dioxide by sulfuric acid method, the turbid titanium liquid is obtained by acid leaching, and the insoluble impurities are mainly the mechanical impurities with larger particles and the colloidal impurities with smaller particles Mechanical impurity is unreacted ferrotitanium mineral, which belongs to coarse dispersion state and is easy to precipitate; colloidal impurity is mainly aluminosilicate, etc., which has the same positive charge due to small particle size and H + adsorption Due to the same charge repulsion, colloidal particles are difficult to get close to larger particles and precipitate, so it has high stability The solution is to neutralize the polyacrylamide colloid with negative charge by electricity to make the colloid particles coagulate and settle However, due to the incomplete settlement of the colloid, after the filtration of ferrous sulfate, some of them still exist in the titanium liquid through filtration The plate and frame filter press with charcoal powder as the filter aid must be used for filtration until the clarity of the filtrate is qualified The most non titanium impurity in ilmenite is iron, which exists in two states of divalent and trivalent The reaction of ilmenite with sulfuric acid produces FeSO4 and Fe2 (SO4) 3 As FeSO4 starts to hydrolyze only when the pH value is greater than 6.5, FeSO4 will remain in the dissolving state all the time during the hydrolysis process of titanium liquid due to the high acidity of titanium liquid, and will be removed during the washing of metatitanic acid However, Fe2 (SO4) 3 begins to hydrolyze to form Fe (OH) 3 precipitate in the acid solution with pH value of 1.7, which is mixed in metatitanic acid When calcined, red brown Fe2O3 is formed, which makes the finished product not pure white So Fe2 (SO4) 3 is reduced to FeSO4 by iron filings In order to ensure that all the trivalent iron in the titanium liquid is reduced to bivalent iron, the reduction reaction should be a little excessive At this time, a small part of the tetravalent titanium in the titanium liquid is reduced to trivalent titanium The existence of trivalent titanium can ensure the complete reduction of trivalent iron, and avoid the hydrolysis of trivalent iron to produce Fe (OH) 3 which will affect the whiteness of the product After reduction, FeSO4 is all in the titanium liquid At this time, when the titanium liquid is frozen, FeSO4 will reach the supersaturated state and a large number of crystals will be separated out Most of the iron can be removed by filtration The remaining amorphous FeSO4 in titanium solution is removed by water washing when metatitanic acid is generated by hydrolysis When the Fe2O3 content of filter cake exceeds 90 × 10-6, the whiteness of product will be affected Therefore, bleaching measures can be taken to reduce the mass fraction of Fe2O3 to 30 × 10-6 and further remove trace impurities such as vanadium, chromium and copper There are still trace iron impurities in the bleached metatitanic acid It is necessary to add 0.1% phosphoric acid to form pale yellow FePO4 to further improve the whiteness of the product In addition to the trace heavy metal impurity ilmenite, it also contains many trace harmful elements When it reacts with sulfuric acid, it can be acidolysis to varying degrees to become soluble sulfate and enter the solution together Through sedimentation and pressure filtration, the undissolved ilmenite residue and aluminosilicate colloidal suspension are basically removed by gravity However, the soluble non-ferrous impurity elements still exist in the titanium liquid, and the following changes take place in the hydrolysis washing: ① some impurity elements do not undergo hydrolysis reaction, do not generate precipitates, and can be removed through the washing of metatitanic acid; ② some elements (including some heavy metal elements), such as antimony, can undergo hydrolysis reaction, and generate white precipitates, which has little effect on the product whiteness; ③ Some colored heavy metal impurity elements (including some rare earth elements) can undergo hydrolysis reaction, forming colored precipitates mixed with metatitanic acid, which ultimately affects the purity and whiteness of the product For example, if there is Nb2O5 in ilmenite, it can enter into TiO2 Crystal when calcined, increasing the semiconductor performance of TiO2 Crystal, leading to the absorption of light, thus affecting the whiteness of titanium dioxide, and having a greater impact on rutile titanium dioxide Therefore, in foreign sulfuric acid production, adding trivalent aluminum to metatitanic acid to compensate the fifth electron of Nb can improve the whiteness of the product Therefore, heavy metals should be removed in the production to avoid the influence of color on the whiteness of the product Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,