| The reserves of readily soluble potassium salts that can be directly utilized in China are seriously short,however,potash resources such as K-feldspar,which are insoluble and not directly usable,are quite abundant.K-feldspar is a kind of aluminosilicate containing potassium framework structure,which has stable physicochemical properties and is not easy to be destroyed.The synthesis of zeolite W is one of the most economical and effective methods for comprehensive utilization of K-feldspar.Potassium-type W zeolite is a kind of small-porosity MER zeolite with low silicon-to-aluminum ratio,which has a typical eight-membered ring main channel structure with three-dimensional interconnection.Due to their special elemental composition and spatial structure,zeolite W is widely used in different fields.In order to reduce the activation temperature and improve the synthesis process of W zeolite,the K2CO3-KOH mixed alkali hydrothermal method and the gel-like-solid phase method were used to synthesize high value-added Potassium-type W zeolite by using respectively chemical raw materials and potassium feldspar as raw materials.The effects of n(K2CO3)/n(KOH),n(Al2O3)/n(Si O2),crystallization temperature and time on zeolite W synthesized by K2CO3-KOH hydrothermal method using chemical raw materials were investigated.The results indicated that high crystallinity and spindle-shaped of zeolite W is synthesized under 150 oC for 15 h with the mole ratio of6K2CO3:20KOH:0.5Al2O3:10Si O2:450H2O.In order to make full use of the elements such as Si,Al and K in the mother liquor after synthetic zeolite,the mother liquor recycling process was designed.After modification,the exchange capacities of modified zeolite W in NH4Cl-(NH4)2C2O4 solution and the simulated seawater were 73.14 mg NH4+·g-1 and 54.31mg K+·g-1,respectively.In view of the large water consumption and complex cycle process of hydrothermal synthesis,a process for synthesizing zeolite W by gel-like-solid phase method using aluminosilicate xerogel(n(Al2O3)/n(Si O2)=0.2)as the silica-alumina source was developed.The results exhibited that zeolite W can be synthesized under a wide range of synthesis conditions:n(K2O)/n(Si O2)=0.125-0.5,n(H2O)/n(Si O2)=5.55-14.81,crystallization temperature T=125-150°C,and crystallization time t=6-18 h.Among them,the bouquet-like shape and well crystallized zeolite W was synthesized under 150°C for 12 h with the mole ratio of n(K2O)/n(Si O2)=0.375 and n(H2O)/n(Si O2)=7.40.The specific surface area of optimal sample is 221.98 m2·g-1,and the NH4+primary exchange capacity in NH4Cl-(NH4)2C2O4 solution is 38.45 mg·g-1 and the highest recovery amount of K+is 52.30 mg·g-1 in simulated seawater.The method greatly reduced the amount of water,shortened the crystallization time,improved the utilization rate of raw materials and simplified the recovery process of mother liquor.What's more,the mother liquor after synthesis of zeolite W could be recycled and used comprehensively,thereby achieving the stable production of zeolite W.The effects of m(K2CO3)/m(KOH),mass ratio of KOH-to-ore,activation temperature and activation time on the K-feldspar activated by K2CO3-KOH fusion method.The suitable conditions for the activation of K-feldspar were as follows:m(K2CO3)/m(KOH)=1.5,mass ratio of KOH-to-ore is 2:1,activation temperature=366 oC,activation time=1.5h.Taking the activated product as a raw material,a reaction precursor with the mole ratio of6K2CO3:20KOH:0.5Al2O3:10Si O2:450H2O was obtained by adding KOH and water.The reaction precursor was statically crystallized at 150°C for 15 h to obtain zeolite W.which is good morphology and spindle shape.The morphology of zeolite W is spindle-shape and the weight percentage of the element of zeolite W is:Si 19.21wt%,Al 11.52wt%,K14.43wt%,O 54.97wt%,which is similar to the composition of zeolite W synthesized from chemical reagents.In order to avoid waste of resources and environmental pollution,the mother liquor recycling process was designed to achieve efficient use of K-feldspar. |
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