Synergistic Enhanced Coagulation Of Fine Gangue By Sodium Alginate And Metal Ions

The efficient and environmentally-friendly treatment of fine particles in tailings is a challenging issue.These tailings are composed of hydrophilic non-metallic minerals such as quartz,kaolinite and calcite.A complex chemical environment is created due to surface dissolution,ion exchange and the addition of flotation reagents.Metal ions present in the slurry not only adsorb onto mineral surfaces,but also impact the molecular conformation of the coagulant and the interaction between the coagulant and mineral particles.Traditional petroleum-based polymer coagulants contain toxic monomers,while natural polymer organics have the advantages of being cheaper,safer,non-toxic and biodegradable.Among them,sodium alginate is capable of flocculation and adsorption,due to the hydroxyl and carboxyl groups present on its molecular chain that can chelate with a variety of metal ions.Therefore,it is of great significance to investigate the reaction mechanism between typical metal ions and sodium alginate,as well as its influence on the coagulation behavior of tailings to develop an efficient,eco-friendly coagulation and settlement process for tailings.In this dissertation,the reaction mechanism between metal ions and sodium alginate was investigated by rheological tests and quantum chemical calculation.The effect of typical metal ions on the dispersion/coagulation behavior between sodium alginate and quartz,kaolinite and calcite were tested by turbidity,FBRM and PVM tests.Further analysis of the interaction mechanism between sodium alginate and these minerals in the presence of different metal ions was performed using zeta potential,FTIR,XPS,and quantum chemical calculations.Finally,this study proposed methods for strengthening the coagulation of gangue particles by sodium alginate and aluminum containing reagents under a variety of metal ion solution environments.The enhanced coagulation measures were verified by using micro coal gangue.The main conclusions are as follows:（1）The reaction mechanism between sodium alginate and Na⁺/Mg²⁺/Ca²⁺/Al³⁺was clarified.The above metal ions lead to macromolecular chain curling because of their electrostatic shielding effect,the apparent viscosity and zero-shear viscosity of the system was reduced.Both Ca²⁺and Al³⁺can react with sodium alginate to form gel,resulting in a sharp increase in the viscosity of the system.Sodium alginate reacts with Ca²⁺to form a high-strength network structure,and sodium alginate reacts with Al³⁺to form a flexible large-scale complex aggregate.It is found that the reaction strength between alginate and metal ions or their hydroxyl complexes from strong to weak as follows:Al³⁺>Al OH²⁺>Ca²⁺>Al（OH）₂⁺>Al（OH）₃>Mg²⁺>Ca OH⁺>Mg OH⁺>Mg（OH）₂>Ca（OH）₂>Al（OH）₄^->Na⁺.（2）The dispersion/coagulation behavior of sodium alginate and Na⁺/Mg²⁺/Ca²⁺/Al³⁺on quartz,kaolinite and calcite were found.Sodium alginate synergistic with Na⁺/Mg²⁺has dispersion effect on quartz and kaolinite particles.Sodium alginate synergistic with Ca²⁺has a dispersion effect on quartz particles,while they have a coagulation effect on kaolinite particles.Sodium alginate and Ca²⁺has more significant coagulation effect on calcite particles than sodium alginate and Na⁺/Mg²⁺.Sodium alginate synergistic with Al³⁺has obvious coagulation effect on quartz,kaolinite and calcite particles under p H 5-7.Sodium alginate complexes with Ca²⁺to form a rigid‘kelp like’gel,which is weak in the ability to trap particles.Al³⁺/Al OH²⁺/Al（OH）₂⁺could cross-links with sodium alginate to form an‘octopus-like’structure,this structure has a high number of tentacles,which could effectively capture particles in water and promote the settlement of particles.（3）The adsorption mechanism of sodium alginate on gangue in the presence of Na⁺/Mg²⁺/Ca²⁺/Al³⁺was revealed.Sodium alginate could adsorb with quartz,kaolinite and calcite particles through hydrogen bonding and electrostatic adsorption.Sodium alginate and Ca²⁺could form chemical adsorption on the calcite and 001 surface of kaolinite.Sodium alginate and Al³⁺/Al OH²⁺/Al（OH）₂⁺could form chemical adsorption on the surface of gangue particles.The electrostatic shielding effect of metal ions on macromolecular chains leads to the reduction of the steric hindrance between molecular chains when metal ions and sodium alginate could not chelate,which increases the adsorption capacity of macromolecular chains on the particle surface and leads to the over-stability of particles.The number of metal ions participating in the electrostatic shielding of macromolecular chains decreased when metal ions and sodium alginate could chelate,resulting in the expansion of macromolecular chains and then the macromolecular traps particles through chemical bridging.（4）The enhanced coagulation law of sodium alginate and Al Cl₃/PAC on gangue particles was explored.In the self-made solution,when sodium alginate and Al Cl₃ were used together,the highest coagulation rate of quartz,kaolinite and calcite suspension reaches 95.1%,89.4%and 91.7%,respectively.When sodium alginate and PAC were used together,the highest coagulation rate of quartz,kaolinite and calcite suspension reaches 97.3%,79.5%and 94.9%,respectively.Compared with sodium alginate synergistic with Al Cl₃,sodium alginate and PAC can not only form an"octopus"structure,but also form a network structure with netting effect.The tentacles of these structures further absorb particles in water through chemical bridging to achieve enhanced coagulation of tailings particles.The actual tailings coagulation results verified the enhancement effect of sodium alginate synergistic with PAC in the coagulation settlement of fine tailings,and the turbidity could be reduced to 25 NTU.This dissertation can provide theoretical support for the development of green and environmentally friendly coagulants and has reference significance for improving the efficient coagulation settlement of tailings and mining wastewater with complex solution chemistry.The dissertation contains 110 figures,36 tables and 227 references.