The Toxicity And Control Of Fluoride Ion On Biological Leaching Of Pickling Waste

In this paper,the bioleaching method of pickling waste and the harmful effects of fluoride ion on the strains during the regeneration cycle were studied.Pickling residue is sediment of neutralizating stainless steel pickling wastewater.That is to join the pickling lime slag settling down a lot of sediment,containing large amounts of heavy metal ions and fluoride ions.In recent years,due to the increase of stainless steel production,pickling residue is gradually increased.Owing to included in the national list of hazardous waste,it can not be directly buried.Therefore,it is urgent to find an environmentally friendly approach.Bioleaching has the advantages of low consumption of acid,low treatment cost,high leaching rate,safety and environmental protection,and no secondary pollution.The biological leaching method is used to treat pickling waste.The bioleaching strains were selected from Acidthiobacillus thiooxidans,Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum,and the cheap sulfur powder and pyrite were used as energy substrates.The pH value was 1.0±0.05.After 6% dosage of pickling sludge were respectively contacted with biological leaching cycle and non-contact leaching cycle,the results showed that the regeneration efficiency of leaching solution after contact leaching was better than that of contact bioleaching.The leaching time was only six hours,which is beneficial to reducing industrial costs.However,the leachate contains a lot of fluoride ions,resulting that the number of leaching cycles is limited to one time and the concentration of nickel is only 1000 mg/L,which can not reach the target concentration.The results showed that the maximum fluoride tolerance was 40 mg/L,and the concentration of fluoride ion should be controlled below 40 mg/L in order to ensure the leaching.The methods used to remove fluoride ions in this paper are chemical precipitation and coagulation sedimentation.First adjust the pH value of leaching solution with calcium oxide 5.0±0.05,then use alum coagulation sedimentation.The dosage is 400 mg/L,which can maintain the fluoride ion concentration below 20 mg/L.This method is better fluoride removal effect,and the use of cheap drugs reduces costs.The experimental results show that the pickling waste residue recycled 11 times and the concentration of nickel can be enriched to 5.1 g/L,fluoride concentration of 37 mg/L.Fluoride concentration did not accumulate.However,when the regeneration cycle was carried out up to 11 times,it was found that with the increasing of the number of cycles,the nickel ion concentration improved and the loss of nickel ions also increased.May be due to calcium oxide and alum fluoride generated during the process of ferric hydroxide colloid,ferrous hydroxide colloid and aluminum fluoride complex increased,a large number of nickel ions to precipitate adsorption,nickel ion loss increased,which is to terminate the cycle s reason.Although the removal of fluoride ions by chemical physical methods can make the cycle go on,it will limit the concentration of nickel ions in a certain range.Therefore,domesticating the existing strains of fluoride-resistant ability or finding new fluoride-resistant strains are fundamental ways to improve the cycle times and enriching rare metals.