Study On The Preparation Of Red Iron Oxide And Nano-magnetic Iron Oxide From Serpentine Acid Leaching Solution

Serpentine is a polymetallic silicate mineral that is high in silicon,magnesium,and iron,and low in nickel,aluminum,and chromium.To use magnesium and nickel in serpentine sulfuric acid leaching solution,impurity metals such as iron,aluminum,and chromium must be removed by neutralization first.The amount of neutralized sludge is large and rich in heavy metals.With the strengthening of the concept of environmental protection,the neutralized sludge needs to be treated.In this paper,it is proposed to use serpentine acid leaching solution as raw material,neutralize and remove impurities to obtain neutralized sludge,use acid leaching-pyrite reduction-purify and remove impurities to obtain ferrous sulfate solution,and then prepare iron oxide red by ammonium bicarbonate precipitation-calcination prepare nano-magnetic iron oxide by direct oxidation and precipitation.The process conditions of each process are studied in detail.Two methods are studied in the purification and removal of impurities in the reducing solution,namely two-step precipitation and one-step purification of pyrrhotite.The main results of the thesis are as follows:Serpentine neutralization slag is prepared by oxidative precipitation of serpentine acid leaching solution.At a temperature of 50℃,the oxidation pH value is 1,and the excess coefficient of H2O2 is 2.2,which can completely oxidize Fe2+ in the serpentine acid leaching solution.Under the conditions of MgO addition speed of 2 mL/min,precipitation pH value of 4,reaction time of 2 h,and stirring speed of 400 r/min,Al,Cr and Fe of the serpentine acid leaching solution can be completely removed to obtain neutralized sludge.The sludge contains 0.92%magnesium,36.8%iron,0.73%nickel,0.03%cobalt,0.09%manganese,3.35%aluminum and 1.28%chromium.The neutralized sludge was dissolved by sulfuric acid,the acid-to-ore ratio was controlled to 1.4 g/g,the temperature was 80℃,and the reaction time was 10 min,the neutralized sludge was completely dissolved to obtain the neutralized slag acid leaching solution.Using natural pyrite to reduce and neutralize Fe3+ in slag acid leaching solution,the influence of key factors on the reduction effect and the phase transformation behavior were studied.In the reaction time of 260 min and the temperature of 85℃,the reduction rate of Fe3+ is 99.99%,and the pH of the reduction solution reaches 2.9.The pyrite aggregates from flakes to large spherical particles.The ion trend behavior,impurity removal mechanism and optimized process conditions of reducing liquid purification and removal were studied.In the two-step purification process,the pH value of the reducing solution was adjusted with NaOH to remove Al and Cr;then Ni,Co and Mn were recovered by Na2S precipitation.When the pH value is 4.2 and the temperature is 65℃,the removal rates of Al and Cr are 99.09%and 98.45%,respectively,and Less Ni,Co,Fe and Mn losses.Under the condition that the excess coefficient of Na2S is 6 and the reaction temperature is 95℃,the recoveries of Ni,Co and Mn are 99.93%,99.72%and 90.1%,respectively,and the loss of Fe is 5.77%.The obtained ferrous sulfate purification liquid has an iron concentration of 37.8 g/L,a nickelcobalt-manganese concentration of less than 7 mg/L,and a nickel content of 13.47%in the nickel-cobalt-manganese precipitation slag,which can be sold as nickel concentrate.Pyrrhotite removes Cr by sulfide precipitation,removes Al by hydrolysis precipitation,and removes Ni and Co by ion exchange.The removal amounts of Ni,Co and Cr from pyrrhotite were 6.49 mg/g,5.48 mg/g and 24.1 mg/g,respectively.By controlling the liquid-solid ratio to be 1.25,the temperature to be 90℃ and the reaction time to be 8 h,the pyrrhotite can completely remove Ni and Co in the reducing solution in one step,the removal rate of Cr reaches 99.56%,and the removal rate of Al was 91.24%.Iron oxide red is prepared from a purified ferrous sulfate solution by ammonium bicarbonate precipitation-calcination process.Adding ammonium bicarbonate with a dosage factor of 1.5 times,reacting at 35℃,pH 7.5 for 5 h,and calcining at 600℃ to obtain iron oxide red,the color is similar to the H101 product of Sanhuan Pigment Company,and the tinting strength is 125.45%.The indicators meet the requirements of category 2 and above of GB/T1863-2008.The two-stage purified ferrous sulfate solution was used to synthesize nano-magnetic iron oxide with tea extract as reducing agent and dispersant.The size of the nanomagnetic iron oxide is 20-60 nm,the saturation magnetic induction intensity is 67.69 emu/g,and the coercivity is 51 Oe.