Preparation Of Nano MoS₂ Adsorbent And Combination Process Of Hypersaline Heavy Metals Removal Fromwastewater

Industrial heavy metal wastewater often possesses salinity to a certain extent.The salt effect leads to difficulty in the removal of heavy metal ions,thus not only restrict industrial production,but also pose a threat to water ecological environment and human health.Aiming at high-salt heavy metal wastewater,screening new adsorbents to develope simple,low-cost,high-efficiency and stable treatment technologies and processes has important application in promoting production and protecting environment.In this study,the nano-MoS₂ adsorbent was prepared by microwave hydrothermal method.The adsorption and removal mechanism of many heavy metal ions were investigated.In addition,the technologies to treat ternary electrode precursor wastewater containing high-salt lithium battery was screened and optimized.The major results of this study were as follows.?1?The microwave hydrothermal method was a fast and low-cost method for preparation of nano-MoS₂.The prepared nano-MoS₂ adsorbent possessed good crystallinity and large surface.The heavy metal ions can be precipitated and removed through the combination between heavy metal ions and sulfur-based active sites on nano-MoS₂ surface.The adsorption order for heavy metal ions was as the result of Mn?II?<Co?II?<Cd?II?<Pb?II?<Cu?II?,which was negatively related to the corresponding solubility product of their sulfides.Using self-made nano-MoS₂ to treat salt-containing heavy metal wastewater,the adsorption effect was affected by the type and content of heavy metal ions and co-existing salt ions,as well as pH of wastewater.?2?The various processing techniques were screened and optimized,aiming at the following characteristics of lithium battery ternary electrode precursor wastewater,ultra-high salinity?TDS 176 g/L?,high ammonia nitrogen?5.96 g/L?,strong alkalinity?pH of 11.5?,and high-level heavy metal?Mn?II?20.5 mg/L,Co?II?15.1 mg/L,Ni?II?262 mg/L?.After secondary enhanced precipitation of NaOH-Na₂S,the residue of Mn?II??<0.10 mg/L?achieved the discharge requirements of battery industrial pollutants?GB 30484-2013?,whilst the concentrations of Co?II?and Ni?II?were reduced to 0.499 mg/L and 0.865 mg/L,respectively.In order to study the main factors affecting removal effect of heavy metals,the simulated wastewater was prepared according to the composition of precursor waste liquid.The result indicated that salinity was the key factor affecting the removal of Co?II?and Ni?II?,and it will be difficult to remove them with the increasing salinity.This result can be explained by the association constant model of Bjerrum.The more higher content of Na₂SO₄was,the larger association constant K_A between Co?II??or Ni?II??and SO₄^2-was.Furthermore,the result of Raman spectroscopy proved the presence of associated ion,which supported the above conclusion.?3?The desalination and deep removal of heavy metal from the precursor waste liquid was performed by the hybrid process of coprecipitation-induced crystallization-capacitor deionization-ion exchange?CPT-IC-CDI-IX?.The induced crystallization unit at 3°C can reduce the TDS from 191 g/L to 68.7 g/L.In the effluent of CDI unit,TDS was decreased to9.9 g/L,while Ni?II?and Co?II?were reduced 0.103 mg/L and 0.172 mg/L,respectively.The concentrations of Ni?II?and Co?II?in the effluent of IX unit were further reduced to 0.0299mg/L and 0.0322 mg/L,respectively,which achieve emission requirement.This hybrid process can recover the hydroxides of heavy metal and large amount of Na₂SO₄ crystals with lower cost and stable effluent.In summary,the synthesized nano-MoS₂ by microwave hydrothermal method has better crystal form and large surface area.However,it was affected by salt ions during the adsorption of heavy metals.The content of Na₂SO₄ in ultrahigh-salinity precursor waste was crucial to remove heavy metal.The hybrid process of CPT-IC-CDI-IX can simultaneously realize desalination and removal of heavy metals,achieving the purpose of resource recovery.This study not only provide theoretical and technical support for the wastewater treatment in lithium battery industry,but also offer a new idea for the treatment of other high-salinity heavy metal wastewater.