Morphology And Structure Of H₂Al₃₀ And Al₃₀ And Monoclinic Na-δ-K-Al₁₃ And The Phase Diagram Of AlCl₃-Al₂O₃-H₂O System At 150℃

The morphology chemistry of aluminum salt hydrolyzates has become a hot and difficult points in many disciplines such as geochemistry,environmental chemistry,biochemistry and water pollution control chemistry etc.The aluminum salt solution is a complex system in which many polymerization forms coexist and change with temperature,basification and composition,although it has been studied as a global hot scientific problem for nearly a century,it still cannot reach a unified understanding on how the monomer aluminum evolves into aluminum hydroxide,how many polyaluminum species exist in the middle,and what evolution process they have experienced.So try to separate various polyaluminum compounds one by one in a single-phase form from the complex hydrolyzed solution,or add a sort of capture agent that could form low solubility compound with a sort of polyaluminum specie in the solution to make the compound isolated from the solution first in a single-phase form,so that to synthesize more polyaluminum compounds and solving their species structures,all these are expected to provide more evidence information to solve this problem.After years of research,our group realized that is a solid-liquid equilibrium problem of aluminum salt hydrolysis and species capture system at different temperatures and pressures,and found the solid-liquid equilibrium phase diagram that is considered to be the most effective control method to date.In this paper,the capture agent is regarded as the fourth component to control the solution composition according to the mind of tetrahedral phase diagram.Four new polyaluminum compounds are precipitated from the forcedly and spontaneously hydrolyzed polyaluminum chloride solutions.The 0.25mol/L AlCl₃ solution was forcedly hydrolyzed by 0.25mol/L and 0.5mol/L KOH solutions at 80°C for 3 days and aged at this temperature for 24 hours to make stock solutions with basification degrees（B=[OH]/[Al]）of 1.4 and 2.0,respectively.7mL and 10mL of 0.1mol/L sodium 2,6-naphthalene disulfonate（2,6-NDS）solution were respectively added into10mL of the above two stock solutions to capture the polyaluminum species,after slowly evaporated and crystallized for 10 days and 3 days at room temperature,Single crystals of two new polyaluminum compounds were obtained.AlCl₃ solution was spontaneously hydrolyzed with Al powder at 100°C for 4 days and aged for 30hours to produce a stock solution of B=1.9,then 20mL of 0.1mol/L Na₂（2,6-NDS）solution was added to the 5mL stock solution,after slowly evaporated and crystallized for 17 days at room temperature,the single crystals of the third new polyaluminum compound were obtained.0.25mol/L AlCl₃ solution was forcedly hydrolyzed by 0.25mol/L NaOH solution at 80°C and aged for 16h to make a stock solution of B=2.0 10mL of 0.1mol/L Na₂（2,7-NDS）solution was added to the 10mL stock solution,after slowly evaporated and crystallized for 20 days at room temperature,the single crystals of the fourth polyaluminum compound were obtained.X-ray structure analysis results show that the first two polyaluminum compounds belong to the same triclinic P1?space group,but the number of interstitial water and unit cell parameters are different.The structural formula and unit cell parameters of the first one are[Al₃₀O₈（OH）₅₈（H₂O）₂₄]（2,6-NDS）₈?48H₂O,a=18.3482（5）?,b=18.6114（5）?,c=19.6949（5）?,α=66.700（1）?,β=64.459（1）?,γ=61.704（1）?,V=5186.2（2）?³,Z=1,D_c=1.765 g/cm³,the unit cell parameters are similar to that of[Al₃₀O₈（OH）₅₆（H₂O）₂₆]（2,6-NDS）₈Cl₂?40H₂O in literature（a=18.5018（12）?,b=18.5823（12）?,c=19.7363（11）?,α=63.414（2）?,β=63.640（2）?,γ=61.977（2）?,V=5116.4（5）?³）;The structural formula and unit cell parameters of the second compound are[Al₃₀O₈（OH）₅₈（H₂O）₂₄]（2,6-NDS）₈?68H₂O,a=18.7998（7）?,b=19.0720（6）?,c=19.8113（6）?,α=63.691（2）?,β=69.259（2）?,γ=67.968（2）?,V=5749.7（4）?³,Z=1,D_c=1.696 g/cm³.The structures of the polycations H₂Al₃₀([Al₃₀O₈（OH）₅₈（H₂O）₂₄]¹⁶⁺)in these two compounds are similar,which can be regarded as the result that the NaO₆ cap in Na─?-K─Al₁₃ was replaced by an AlO₆cap forming an Al─?-K─Al₁₃,then two Al─?-K─Al₁₃ groups were connected together by two AlO₆ monomers through vertex-sharing,it is similar to the structure of“Al₃₀”([Al₃₀O₈（OH）₅₆（H₂O）₂₆]¹⁸⁺)in the aforementioned literature,however,its composition and charge are different,it is equivalent to the result that the―Al₃₀‖was further hydrolyzed and two protons were removed.Because the anions reported in the literature have two Cl^-ions in addition to eight[2,6-NDS]^2-,however,EDS analysis proves that neither of the two compounds obtained in this paper contains chlorine.So the 18 positive charges carried by―Al₃₀‖cannot be balanced by the eight[2,6-NDS]^2-anions only,that is to say,the polycation H₂Al₃₀ in these two products has only 16positive charges,it requires that two protons on―Al₃₀‖should be removed by hydrolyzing.According to the principle of local basification degree symmetrical equalization（LBDSE）proposed by our group,the hydrolysis and polymerization reaction always happen in the place where the local basification degrees are the most un-equalized in symmetries.It can be presumed that the positions with the highest hydrolysis activities in―Al₃₀‖should be the first and second class hydrolysis active areas on both sides of the waist（see Figure 3.11 in the main text）.When the hydrolysis reaction to remove two protons only occurs on the two coordinating H₂O molecules in the first-class active area,it is the structural manner of H₂Al₃₀ in these two compounds.The third compound also belongs to the triclinic P1?space group,but its structural formula and unit cell parameters are completely different from the first two,namely[Al₃₀O₈（OH）₆₀（H₂O）₂₂]（2,6-NDS）₆Cl₂?48.5H₂O and a=16.2445（11）?,b=21.0380（14）?,c=22.4933（15）?,α=99.723（1）?,β=108.257（1）?,γ=108.517（1）?,V=6603.5（8）?³,Z=1,D_c=1.524 g/cm³.Since there are only six[2,6-NDS]^2-and two Cl^-ions in the compound,the polycation Al₃₀([Al₃₀O₈（OH）₆₀（H₂O）₂₂]¹⁴⁺)can carry 14 positive charges at most,the structure of which is equivalent to the result that H₂Al₃₀ was further hydrolyzed by removing the two protons in the second-class hydrolysis active area,the difference with D-Al₃₀([Al₃₀O₈（OD）₆₀（D₂O）₂₂]¹⁴⁺found by our group)is that when a H was removed from one of the two adjacent coordination H₂O molecules,the other H₂O has not shared its H（that statistically occupies two sites）with the OH^-group formed after deprotonating.This is another example that the coordination water molecules in both the first-and second-class hydrolysis active areas were partly hydrolyzed.Both H₂Al₃₀ and Al₃₀ are all the result that―Al₃₀‖reduces its un-equalization degree by hydrolyzing at its waist where the local basification degrees are the most un-equalized in symmetries,it is consistent with the expectation of the LBDSE principle.Therefore,it can be presumed that the 18 charged―Al₃₀‖which maintained high hydrolysis activities but had not been hydrolyzed could not exist stably,the two Cl^-ions used to balance the charge are probably interstitial H₂O molecules in the literature.The fourth polyaluminum compound belongs to monoclinic P2₁/c space group,a=27.4287（4）?,b=21.0100（3）?,c=36.7347（5）?,β=119.9490（2）?,V=18342.6（5）?³,Z=8,D_c=1.794 g/cm³,the structural formula is[NaAl₁₃O₄（OH）₂₄（H₂O）₁₅]（2,7-NDS）₄?12H₂O.In which the structure of the polycation Na─?-K─Al₁₃([NaAl₁₃O₄（OH）₂₄（H₂O）₁₅]⁸⁺)can be regarded as that one of the four Al₃ units（three AlO₆ octahedra connected with each other by vertex-and edge-sharing）that respectively connected to the four vertexes of the central AlO₄tetrahedron by vertex-sharing in?-K─Al₁₃ was rotated 60?around the line linked their center and the shared vertex,then a NaO₆ octahedral cap is capped on the outside of the triangular pit of the rotated Al₃ unit.It is similar to the structure of Na─?-K─Al₁₃3 in[NaAl₁₃O₄（OH）₂₄（H₂O）₁₅]（SO₄）₄?16H₂O and[NaAl₁₃O₄（OH）₂₄（H₂O）₁₅]（2,6-NDS）₄?10.5H₂O belonging to triclinic P1?space group in literatures,but the counteranions,crystal systems,space groups,and unit cell parameters of their compounds are completely different,it is a new polyaluminum compound.This monoclinic naphthalene disulfonate of Na─?-K─Al₁₃ phase with superlarge unit cell enriches the crystallization method of Na─?-K─Al₁₃ species.The discovery of above four polyaluminum species structures not only provided an important support for proposing the evolution course from Na─?-K─Al₁₃ to Al_30.5,but also further verified the scientificity of the LBDSE principle in predicting the active sites of hydrolysis reaction and guiding the structure solving process;Not only had a deeper understanding to the applicability of sodium naphthalene disulfonate as a crystallization agent to capture polyaluminum species,but also obtained a deeper understanding to the formation and transformation rules of aluminum species in hydrolyzed aluminum salt solutions,and also played an important role for communicating the relationship between spontaneous hydrolysis and forced hydrolysis.In this paper,the solid-liquid equilibrium isothermal phase diagram of AlCl₃-Al₂O₃-H₂O system under 150°C hydrothermal conditions were also successfully measured by combining the wet slag method and the synthesis system method,using the special functions of the preparation-type high-pressure reaction kettle system（which can be operated for filtering and sampling online,distilling and concentrating,and feeding online）designed and customized by our group.Also,the capacity and weight analysis methods used in the past were replaced by solution X-ray fluorescence method,which greatly improved the efficiency of analysis and testing.It not only provides a control basis for designing synthetic routes to prepare Al₁₇O₁₆（OH）₁₆Cl₃ and AlOOH that can be separately precipitated at this temperature,but also lays a good foundation for measuring the tetrahedral phase diagram of the four-component system including the capture agent under 150°C hydrothermal conditions in the future.