| Rich high Mg/Li ratio salt lake brine of Qinghai salt lake in China is the major resources of lithium and magnesium.The technique of suiting for the lithium-magnesium separation and extraction process from high Mg/Li ratio salt lake brine,low energy consumption and environmentally friendly is still need to be tackled.In several methods extraction of lithium from brine,the precipitation method is the simplest process because of low energy consumption,low pollution and low cost.However,it is not suitable for high Mg/Li ratio salt lake brine.Therefore,the ratio of magnesium to lithium must be reduced firstly before using the precipitation method to extract lithium from high Mg/Li ratio salt lake brine.The value solubility product constant of magnesium hydroxide is very small,while lithium hydroxide is soluble.So the magnesium ions can be precipitated by hydroxide,and the purpose of removing magnesium and reducing the ratio of magnesium to lithium are achieved.But the directional rate of nucleated ions of the magnesium hydroxide precipitate is small,however,the aggregation rate of glue core is high,which is bridged by hydroxides to form the colloids with high degree of hydration.Therefore it's difficult to achieve the solid-liquid separation of magnesium hydroxide and lithium magnesium separation in the process.In this paper,the removing magnesium reaction by precipitation method was improved,and the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid was synthesized,which is similar to the structure of the magnesium reagent.Using the sodium hydroxide as main precipitant and the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid as auxiliary precipitant,they were compounded to obtain compound precipitant.Based on the exploration of the precipitation method for separation of lithium and magnesium in high Mg/Li ratio salt lake brine by using the compound precipitant and the preparation of magnesia porous materials by the precipitation of magnesium hydroxide,the following results were obtained:?1?Under the conditions of raw material mole ratio,namely n?sulfanilic acid?: n?sodium nitrite?: n?sulfuric acid?: n?phenol?= 1:1.2:3:1,diazotization reaction at 2 ?-3 ? for 3 h,azo reaction under weak base for 3 h,the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid was synthesized with the yield of 85.26 %.The melting point was measured at 314.8? after purification by recrystallization,melting range??T = 0.3 ??was narrow,it indicated high purity of synthetic product.The theoretical vibration frequency and theoretical IR spectrogram were calculated by using Gaussian software,compared with the actual IR spectrogram,the synthesized product was identified as the target molecule.And the structural characterization of the target molecule was confirmed by mass spectrometry,nuclear magnetic resonance spectroscopy and ultraviolet spectroscopy.?2?The selectivity of the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid to magnesium ions was investigated.It was applied to five different metal ion solutions of lithium ions,sodium ions,potassium ions,magnesium ions and calcium ions,which only form precipitate with magnesium ions.When the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid was reacted on the high Mg/Li ratio simulated brine,it has a good selective precipitation effect on magnesium ion.The selectivity coefficient of the magnesium ions is 416.72,while the selectivity coefficient of the lithium ions is only 0.0024.?3?Sodium hydroxide as the main precipitant and the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid as auxiliary precipitant were compounded to obtain compound precipitant.The separation of lithium and magnesium in high Mg/Li ratio simulated brine by using the compound precipitant was studied.The effect of precipitation method of using compound precipitant was evaluated by filtration rate,magnesium removal rate and lithium loss rate.The results showed that the optimal conditions for removing magnesium with compound precipitant were as follows: at the reaction temperature of 60 ?,positive drops,40 ml of sodium hydroxide solution with 2 mol·L-1,1% of the relative amount of the main precipitant as the addition amount of the 4-??4-hydroxyphenyl?diazenyl?benzenesulfonic acid,adding sodium dodecyl benzene sulfonate as the dispersant to the high Mg/Li ratio simulated brine???Mg2+?=90 g/L;??Li+?=3 g/L;Mg/Li=30?.The filtration rate of the solid-liquid separation after the reaction was increased from 0.56 m L·min-1 by directly removing magnesium with sodium hydroxide to 3.86 mL·min-1,whith was increased to the original 7 times.The magnesium removal rate was 100%,and the magnesium ions were precipitated completely.The lithium loss rate was reduced from 21.20 % by directly removing magnesium with sodium hydroxide to 1.78 %.The magnesium hydroxide precipitate with reunion less,easier to filter,uniform particles and complete crystal form was obtained.?4?The preparation of magnesia porous materials for the magnesium hydroxide obtained by the precipitation method was studied.The obtained magnesium hydroxide was calcined at high temperature into magnesium oxide.Using solid sintering method,adding pore-forming agent,adhesive and sintering additives with a certain proportion,by ball milling,molding,drying and sintering,magnesia porous materials were prepared.The preparation conditions of the types of pore-forming agents,the amount of pore-forming agent,sintering temperature and sintering auxiliaries were explored,and the performance of the resulting material was characterized,the optimum conditions for the preparation of magnesia porous materials were as follows: Using starch as the pore former with the addition of 35%,silica as the sintering additive with the addition of 5%,polyvinyl alcohol as the binder,at the sintering temperature of 1200 ?.The magnesia porous materials with the porosity of 63.90 %,the bulk density of 1.14 g.cm-3,the compressive strength of 5.47 MPa and the thermal conductivity of 0.0506 W·?m·K?-1 were obtained. |
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