Characteristics Of Secondary Aluminum Dross And Research And Application Of Its Total Resource Utilization

Secondary aluminum dross(SAD)is a solid waste discharged after aluminum extraction from aluminum slag.SAD is classified as HW48 hazardous waste due to containing aluminum nitride(AlN)and salts.Over 2 million tons of SAD is produced in China in 2021,which restricts the development of aluminum industry.Therefore,harmless disposal and resource utilization for SAD is the key technology,which is urgently needed by aluminum industry.AlN and salts are removed by washing in current disposal technologies,which produces hazardous ammonia and salty wastewater.Therefore,it is urgent to develop a novel green resource utilization technology for SAD.This work was conducted based on the above significant requirements.Characteristics of SAD were studied.According to its reducibility and resource characteristic and dual ion reaction mechanism in aluminosilicate melt,we developed the technology of SAD reducing heavy metals followed by manufacturing glass ceramics and calcium aluminate refining agent for steel.This work realized the total resource utilization of SAD.The main conclusions were following:(1)This work developed the technology of SAD reducing heavy metals in picking sludge.AIN in SAD was the main reductant.Reduction rates of Fe,Cr and Ni was up to 97%,91%and 100%,when mass ratio of SAD to picking sludge was 1:2.Weight of the obtained alloy was up to half of SAD.A ton of SAD replacing carbon to reduce heavy metals could reduce carbon emission of 279 kg.(2)This work studied the oxidization competition reactions for AlN in SAD.AlN could be oxidized by oxygen in air during reducing heavy metals.Oxidization was reduced after shortening melting time,and heavy metals reduction rate was increased from 51%to 86%.Oxidization was reduced significantly after cutting off air,and heavy metals reduction rate was increased from 48%to 92%.In addition,CaF2 and soda could corrode alumina protective layer on AlN.Oxidization was exacerbated after adding CaF2 and soda,and heavy metals reduction rate was decreased from 48%to 19%.(3)This work studied the mechanism of AlN reducing heavy metals.Reduction reaction consisted of two steps:heavy metals and AlN entered aluminosilicate slag;homogeneous reduction reaction occurred.The reduction reaction was heterogeneous reaction before AlN and heavy metals entered slag,and it possessed a low reaction rate.The reaction turned into homogeneous reaction after AlN and heavy metals entered slag,and reaction rate increased significantly.According to the homogeneous reaction,this work proposed a novel pyrometallurgy homogeneous reaction environment of aluminosilicate melt’solution’ and a novel dual ion reaction mechanism in aluminosilicate melt.(4)This work developed the technologies of manufacturing glass ceramics and calcium aluminate refining agent for steel from SAD.AlN in SAD was oxidized into alumina by heavy metals or oxygen,followed by manufacturing glass ceramics and refining agent.Bending strength,microhardness and alkali resistance of the glass ceramics were up to 77 MPa,1011 HV and 98.7%.Composition of refining agent met the industry standards.And the refining agent possessed a stable physical and chemical properties after being manufactured in air atmosphere.Manufacturing a ton of glass ceramics and refining agent from SAD could gain profit of 1368 and 475 yuan,and reduce carbon emission of 499 and 835 kg.