Experiment Research On Recovery Of Spent Pickling Solutions With Vacuum Distillation

In pickling process,steel will produce a large amount of spent pickling solutions?SPS?,which mainly contains high concentrations of ferrous salts and residual acid,which far more than the the emission concentration limits.Direct emission will not only do great harm to human health and ecological environment,but also Caused a lot of waste of resources.In general,the spent pickling solutions treatment process includes a chemical method and a physicochemical method,and includes a high-temperature calcination method,an iron salt crystallization method,an extraction method,a neutralization method,an ion exchange method,and a membrane treatment method.This subject has studied the vacuum distillation process that is more suitable for small and medium-sized enterprises,and recycles and uses the hydrochloric acid spent pickling solutions,and hopes to provide guidance for the application of industrialization.The process includes several stages:firstly,the waste acid is pretreated,excessive broken iron is added and then filtered;the waste acid after filtration is subjected to negative pressure distillation,and the distillate is condensed to form regenerated hydrochloric acid;and the evaporated concentrate is cooled and crystallized.Finally,the crystals were centrifugally dehydrated and packaged.For this process,this article has carried out several aspects of research:1)the components of the waste acid system under study were firstly analyzed by different test methods.The physicochemical properties such as density and boiling point,acid concentration,concentration of various salt components mainly composed of ferrous ions,etc.were measured.The total iron concentratio n was 137.9g/L,the acid concentration was 2.1mol/L,and the chloride ion concentration was 183.14g/L.The concentration of total iron and other pollutants far exceeded the emission concentration limit.2)an atmospheric distillation experimental device was designed to examine the compositional changes,crystal precipitation,and distillate production of the acid-washing wastewater during the evaporation process.The experimental results show that the COD in the distillate and the total The concentration of nitrogen and total iron continues to decrease.The water in the spent acid liquor continuously evaporates.The concentration of ferrous ions continues to condense to saturation.After cooling,a large amount of ferrous chloride crystals are precipitated,and the 200mL of hydrochloric acid waste acid is concentrated to 70mL,which is the evaporation ratio.At 65%,the amount of precipitated crystals reached 77.04g and the crystal purity reached 97.1%.3)In order to perfect and validate the pilot experiment,the Aspen Plus chemical simulation software was used to simulate the negative pressure evaporation process of the hydrochloric acid spent pickling solutions,and a negative pressure evaporation-cooling crystal recovery hydrochloric acid waste acid liquid system model was established.A large amount of regenerated hydrochloric acid was obtained.And high purity ferrous chloride crystals.According to the simulation results,after evaporating 1 kg of water,600 g of crystals are precipitated after the evaporation mother liquor cools.The purity of the ferrous chloride crystals is more than 96%,and the hydrochloric acid recovery rate is about 30%.When the evaporation ratio increases,the cooling rate increases.During the process,zinc chloride crystals began to appear,affecting the purity of ferrous chloride crystals.Considering the evaporation efficiency,acid regeneration rate and process cost under different vacuum levels,the evaporation ratio is 60%and the vacuum degree is 0.065MPa which are the best working condition,when W/D value is about 1.6kg·kW^-1·h^-1.4)the negative pressure distillation process was used to carry out the engineering test of hydrochloric acid pickling waste in a workshop of a tower factory,and a wastewater treatment station with a treatment scale of 6m3/d was designed.The processing station adopts the vacuum distillation process,adding excess iron scraps to the waste acid and then filtering.The pre-treated hydrochloric acid waste acid enters the vacuum evaporation plant for batch distillation.The heat source is the gas boiler steam,and the single batch enters The material is 2m³ and 3 batches of waste acid are processed every day for a total of 7.5h/d.According to the results of the operation,it is known that for every 1m3 of waste acid that is evaporated,about 62kg of crystals and0.4 m³4%of regenerated acid can be recovered,and the purity of the recovered ferrous chloride crystals is in accordance with the standards o f HG/T 4200-2011.The annual operating cost of the waste water treatment station was 307,600yuan/year,which was converted into treatment cost,that is,140.45yuan/m³ waste acid,far lower than the price of the spent pickling solutions market.The process realizes the recycling and utilization of hydrochloric acid pickling waste liquid,which not only solves the problem of waste acid liquid pollution to the natural environment,but also recovers dilute hydrochloric acid and ferrous chloride crystals,turns waste into treasure,and reduces processing cost,which is with good economic and environmental benefits.