| The distribution of potash resources is extremely uneven in China.Most of the soluble potassium salts are distributed in salt lakes of the northwest and southwest China,where the climate is harsh and transport is underdeveloped.At the same time in the developed agricultural areas of the central and eastern China,the natural potassium resources are extremely scarce,where the potash demand is huge.It is valuable to recycle and re-use potassium from some industrial and agricultural byproducts wastewater,tailings wastewater of alkali metal mines and even seawater.Therefore,the process of recycling potassium from potassium-containing solution is extremely important for relieving the shortage of potassium salt.Mechanochemical activation is a common method to control the degree of reaction by adjusting the intensity of mechanical force,with green and efficient advantages.On the other hand,hydroxyl groups are the most active functional groups of minerals.Therefore,based on Mechanochemical method,the characteristics and mechanism for adsorption and separation of potassium by using hydroxyl-rich minerals such as kaolin,Mg-Al LDH,serpentine and gibbsite were studied.A new type of potassium adsorption material was prepared,and the separation between K/Cs and K/Na was successfully realized,which provided a new way for recycling and utilization of alkali metal resources,and had all-important academic value.Based on mechanochemical method,the reaction characteristics of phosphoric acid and kaolin by ball-milling were studied.In the case of modification kaolin by phosphoric acid(KP),part of the free hydrogen ion in phosphoric acid was combined with the hydroxyl groups in the kaolin structure,leading to the production of water molecules.So that phosphoric acid was fixed onto amorphized kaolinite with Si-O-Al-P bound.The adsorption capacity of potassium ion reached about 6 mg/g from a low concentration solution.The adsorbent provided a new option for recovering potassium from seawater and tailings wastewater.Then,based on the adsorption characteristics of potassium ions by using KP materials,the effects of Mg-Al LDH and activated serpentine on the adsorption of potassium by KP were studied.The results showed that Mg-Al LDH had a synergistic effect on the adsorption of potassium ions by KP materials.The synergistic mechanism was that Mg-Al LDH adsorbs anions,and the exchanged OH~-consumed the accumulation of H~+exchanged by KP materials,promoting the continuous adsorption reaction of potassium ion.The adsorption performance of KP materials was significantly improved and the saturated adsorption capacity of potassium ions was 28.47 mg/g.Activated serpentine had a promoting effect on the adsorption of potassium ions by KP materials.The mechanism of promotion was that the hydroxyl group in the structure of antigorite was continuously dissolved under the action of mechanical activation,which consumed H~+generated during the process of KP adsorption of potassium,and promoted the adsorption reaction.The saturated adsorption capacity of potassium ions was as high as 32.46 mg/g.It also indicated that the new adsorbent materials were effective for different types of potassium salts.The adsorption effect of carbonate was particularly desirable.In addition,the synergistic adsorption of potassium maintained a stable adsorption performance in acidic environment.The differences were that Mg-Al LDH simultaneously adsorbed anions,and a composite fertilizer could be prepared by using available anion such as ammonia nitrogen in the solution environment.While,the activated serpentine did not bring in anions,which avoided acidification of the soil,and provided new ideas for solving related problems in the field of resources and environment.Finally,based on the large difference in reaction characteristics of alkali metal elements in mechanochemical reactions,the separations of K-Cs and K-Na were studied.The difference in reaction characteristics between serpentine-K and serpentine-Cs ions indicated that in a near-neutral environment,the mechanically activated serpentine acted as a carrier nucleus,and the Mg active site on the surface reacted with the strontium ions and phosphate ions in the solution to form a struvite crystal structure and precipitated rapidly,while the potassium ions remained in the aqueous solution.The mechanically characteristics of K and Cs ions were not found in conventional chemical reactions.The process was of great significance for the recovery and utilization of potassium in the tailings wastewater.The difference in reaction characteristics between gibbsite-K and gibbsite-Na indicated that the gibbsite would react with K ions in a low-temperature hydrothermal environment to form potassium alunite precipitates under mechanical activation,while sodium ions with relatively small ionic radius did not participated in the reaction.The process effectively realized the separation of potassium and sodium,and had a great application value. |
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