Process for producing kaolin product for paper coating

A process for producing a kaolin product for paper coating comprising:

• (a) mining kaolin ores by hydromechanization and then producing kaolin slurry;
• (b) classifying by centrifugal sedimentation, wherein the kaolin slurry obtained from the former step is classified with a horizontal spiral sedimentation machine;
• (c) chemical bleaching, wherein the kaolin slurry classified by centrifugal sedimentation is bleached;
• (d) eliminating iron ions by circular rinsing, wherein the kaolin slurry is washed by circular rinsing and dewatered after it has been bleached through the chemical bleaching and then slurry G is obtained;
• (e) removing water by pressure filtration, wherein the kaolin slurry G is filtered under pressure to remove water and filter cakes, which contains 32 wt. %-35 wt. % water and has a pH value of 4.3-5.9, fall into a dispersing pond;
• (f) producing slurry by deflocculating, wherein complex dispersants, pH adjusting agent and intercalator are added into the filter cakes;
• wherein the complex dispersants are sodium polyacrylate and sodium hexametaphosphate, the pH adjusting agent is sodium hydroxide and the intercalator is urea;
• wherein the sodium polyacrylate has a molecular weight of 1300-2000, and is added in 1 wt. %-3 wt. % of the dry weight of the filter cakes;
• the sodium hexametaphosphate is added in 2 wt. %-3 wt. % of the dry weight of the filter cakes;
• the sodium hydroxide is added in 3 wt. %-4.5 wt. % of the dry weight of the filter cakes;
• and the urea is added in 2 wt. %-6 wt. % of the dry weight of the filter cakes;
• and the kaolin slurry is stirred and dispersed to obtain kaolin slurry H whose solid content is 56 wt. %-62 wt. % and pH value is adjusted to 6.3-7.0;
• (g) delaminating, wherein the kaolin slurry H is added into vertical agitated mills containing a particulate grinding medium and delaminated by stirring, to obtain kaolin slurry I whose solid content is 56 wt. %-62 wt. %;
• (h) classifying by vibrating sieve, wherein the kaolin slurry I is passed through two layers of 325-mesh vibrating sieves to obtain kaolin slurry J;
• and
• (i) spay drying, wherein spray driers are modified by adding insulating layers on packing auger, elevator scoop and bunker at first;
• the kaolin slurry J which has been passed through vibrating sieves is dried in high speed centrifugal spray drying tower where the parameter of fresh feed pump is 3.5-4.0 Hz, the temperature of spray drying of the high speed centrifugal spray drying tower and the temperature at the outlet are set to 230-380° C. and 60-85° C. respectively, and the moisture of kaolin powder is controlled in 3 wt. %-5 wt. %;
• and the intercalation reaction of the kaolin slurry is performed in the process that the powder passes through the packing auger, the elevator scoop and the bunker, and the kaolin product for paper coating is obtained after the intercalation reaction.