Molecular Design Of N-substituted Hydroxamic Acids And Their Flotation And Extraction Performances

To address the problems of the efficient and clean utilization of strategic mineral resources such as tungsten,tin and copper in China,Nsubstituted hydroxamic acids were designed and synthesized and their flotation and extraction performances were systematically studied by using the theories of quantum chemical calculations,structure-activity relationship analysis and interface chemistry.Therefore,this study is of great significance to promote the development of tungsten,tin and copper beneficiation agents.N-phenylethyl hydroxamic acid(NPHA-2),N-phenylbutyl hydroxamic acid(NPHA-4),N-phenylhexyl hydroxamic acid(NPHA-6),Nphenyloctane N-phenyldodecyl hydroxamic acid(NPHA-8),Nphenyldodecyl hydroxamic acid(NPHA-12),N-benzylethyl hydroxamic acid(NBHA-2),N-benzylbutyliso Hydroxamic acid(NBHA-4)and Nbenzyloctyl hydroxamic acid(NBHA-8)were designed from benzohydroxamic acid(BHA)and salicylaldoxime(SAO)through the principle of isomerism and structural modification.The flotation and extraction performances were scientifically evaluated and predicted by quantum chemical simulation calculations and hydrophobic performance experiments.The calculation results showed that the Z-form was the most stable form of the two isomers of N-substituted hydroxamic acids.The negatively charged areas were mainly concentrated on the C=O and-OH groups,and the two oxygen atoms with lone pair electrons readily donated electrons to the empty orbital of the metal to form a coordination bond,thereby forming coordination bond with the metal ion on the mineral surface.chelation.N-substituted hydroxamic acids showed stronger chemical activity and electron donating ability than benzhydroxamic acid(BHA),which may possess better flotation performance.Meanwhile,since the aryl group was directly connected to the N atom of N-substituted hydroxamic acid,less negative charges were concentrated on the N atom,while the charge configuration similar to SAO made N-substituted hydroxamic acids possibly possess certain extraction performance.Compared with N-benzyl hydroxamic acids,N-phenyl hydroxamic acids possessed certain advantages in dipole moment and chemical activity.The results of the studies on solubility and hydrophobicity showed that the hydrophobic performances of N-substituted hydroxamic acids increased with the increase of non-polar carbon chains.N-phenyl hydroxamic acids were synthesized using nitrobenzene as the primary material by reactions of reduction and acylation.The total yields after two steps reactions of NPHA-2,NPHA-4,NPHA-6,NPHA-8 and NPHA-12 were 84.86%,82.44%,81.65%,75.78% and 80.14%,respectively.N-benzyl hydroxamic acids were synthesized using benzaldehyde oxime as the primary material by reactions of reduction and acylation.The total yields after two steps reactions of NBHA-2,NBHA-4 and NBHA-8 were 64.59%,63.01% and 62.18%,respectively.Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance(NMR)analysis were adopted to characterize the structures of the synthesized N-substituted hydroxamic acids.The flotation performances and interaction mechanisms of Nsubstituted hydroxamic acids for cassiterite and wolframite were systematically investigated.The flotation performances of N-phenyl hydroxamic acids for cassiterite became stronger with the growth of nonpolar carbon chain.Among them,NPHA-8 possessed the best flotation performance for cassiterite.At p H = 7,the flotation recovery of cassiterite was up to 95.94% with a dosage of 50 mg/L,significantly stronger than BHA,which can realize the effective separation of cassiterite from quartz and feldspar.The interaction mechanisms between NPHA-8 and cassiterite were studied by the adsorption experiments,contact angle analyses,Zeta potential tests,FTIR and X-ray photoelectron spectroscopy(XPS)analyses.The results showed that NPHA-8 could chelate with the tin atoms and interact with the positively charged species on the surface of cassiterite through electrostatic attraction.The strong hydrophobic performance of NPHA-8 ensured its excellent collecting ability for cassiterite.In addition,NPHA-8 showed strong collecting ability for wolframite without adding foaming agent or activator.At p H = 7,NPHA-8 could float 96.21%wolframite with a dosage of 50 mg/L.NPHA-8 could effectively separate wolframite from quartz and fluoritet,while the separation efficiency was better than BHA and octyl hydroxamic acid(OHA).The results of the adsorption mechanism study showed that NPHA-8 chelated with the composition of iron on the surface of wolframite through the C=O and-NOH groups to form a stable five-membered-ring complex.The flotation performances and interaction mechanisms of Nsubstituted hydroxamic acids for copper oxide minerals were systematically investigated.N-substituted hydroxamic acids with short non-polar carbon chain possessed strong separation performances for malachite and calcium gangue minerals.At the optimal p H,the recoveries of malachite by using NBHA-4 and NPHA-4 with a dosage of 200 mg/L were over 80%,while those of calcite and quartz were below 30%,obviously better than BHA.The effect of NBHA-4 on the surface hydrophobicity of malachite was studied by the contact angle experiments.The results showed that the surface hydrophobicity of malachite treated by NBHA-4 noticeably improved,while that of calcite and quartz were relatively unaffected.The results of the adsorption experiments showed that the adsorption capacity of NBHA-4 on calcite or quartz was much lower than that of malachite.The interaction mechanisms between NBHA-4 and malachite were studied by solution chemistry,FTIR and XPS analyses.In addition to the electrostatic interaction between NBHA-4 and the malachite surface,NBHA-4 could chemisorb onto the malachite surfaces through the reactions of the C=O and-NOH groups and the formation of a five-membered-ring complex.No significant chemisorption was detected on the calcite and quartz surfaces,resulting in the efficient separation of malachite from quartz and calcite.The extraction performances of N-substituted hydroxamic acids were investigated by using NPHA-8,NPHA-12 and NBHA-8 as the extractants.At the experimental p H,N-substituted hydroxamic acids showed good extraction ability for copper ions and certain extraction ability for iron ions,while the extraction abilities for manganese ions,calcium ions,cobalt ions and nickel ions were very poor.Therefore,the extraction performances of Nsubstituted hydroxamic acids for copper ions were further studied.The effects of extraction time,aqueous p H,extractant concentration,phase ratio and initial copper ion concentration on the extraction process were studied and compared with Mextral 984 H.The results showed that NPHA-8 and NPHA-12 possessed strong extraction ability for copper ions,while the extraction ability of NPHA-8 for copper ions was slightly weaker than Mextral 984 h and stronger than NPHA-12.Compared with Mextral 984 H,the stripping abilities of NPHA-8 and NPHA-12 were stronger.In addition,NPHA-8 could effectively separate copper ions from cobalt ions and nickel ions,better than Mextral 984 H.The results of ultraviolet spectroscopic analysis and quantum chemical calculation showed that NPHA-8 was easy to chemically react with the copper ions,but possessed a weak interaction with manganese,calcium,cobalt and nickel ions,leading to its strong extraction and separation performances for copper ions.