Removal Performance And Mechanism For Chromium And Manganese From Water By Dithiocarboxyl Hydroxymethy-Polyacrylamide

Heavy metal pollution has become one of the most serious environmental problem,with the development of industrial production,chromium-containing wastewater has become a threat to the our society and human health.Hexavalent chromium and trivalent chromium can be accumulated in animals and plants,which leads to serious pollution to the environment,and a long-term impact on human health.thus it can be seen that the harm caused by manganese-containing wastewater has become a serious problem that can not be ignored.In this research,dithiocarboxyl hydroxymethy-polyacrylamide（DTMPAM）is used as a macromolecule flocculant,we assess the performance of DTMPAM in removal of Cr（Ⅵ）and Mn（Ⅶ）.The effects of DTMPAM dosage,pH value,initial concentrations of Cr（Ⅵ）or Mn（Ⅶ）,coexisting turbidity,inorganic substances and organic substances on the performance of DTMPAM in removal of Cr（Ⅵ）and Mn（Ⅶ）in water samples,respectively.The mechanism in the removal of Cr（Ⅵ）and Mn（Ⅶ）in water samples with the assistance of DTMPAM is revealed by infrared analysis,scanning electron microscopy and energy spectroscopy.The main experimental results are as follows:（1）DTMPAM has good removal efficiency on different initial concentrations of Cr（Ⅵ）in water samples under acidic conditions.When the pH value is 3.0 and the best hydraulic conditions are set as fast stirring speed of 160 r/min,fast stirring time of 2.5 min,slow stirring speed of 40 r/min,slow stirring time of 5 min,and sedimentation time of 10 min,the highest Cr（Ⅵ）removal rate reached 94.78%,96.52%,96.53%and 97.49%,respectively,corresponding with initial concentration of Cr（Ⅵ）of 5 mg/L,15 mg/L,25 mg/L and 50 mg/L in water samples.（2）When the dosage of DTMPAM is lower than 420 mg/L,the coexistence turbidity has a certain inhibitory effect on the removal of Cr（Ⅵ）by DTMPAM.When the dosage of DTMPAM is higher than 420mg/L,the coexisting turbidity has almost no effect on the removal of Cr（Ⅵ）by DTMPAM.Inorganic ions,such as K⁺,Na⁺,Ca²⁺,Mg²⁺,Fe³⁺,Ni²⁺,Ba²⁺,SO₄^2-,Cl^-,NO₃^-,F^-,I^-,Br^-,IO₃^-,Br O₃^-,and organic substances,such as sodium citrate,sodium acetate,trichloroacetic acid,sulfamic acid and aminoacetic acid had different effects on the removal of Cr（Ⅵ）and total chromium under different dosages of DTMPAM.Infrared spectroscopy and energy spectrum analysis indicated that the dithiocarboxyl group on the DTMPAM molecular chain could reduce dithiocarboxyl group and amine group on the DTMPAM molecular chain to form flocs.（3）The removal rate of Cr（Ⅲ）by DTMPAM at pH 3.0,4.0,5.0 and 6.0 respectively reached23.80%,41.11%,42.38%and 86.01%,which was not satisfactory.The dosing sequence and initial concentration of FeCl₃had a great influence on the removal of Cr（Ⅲ）by DTMPAM compounded with FeCl₃,and the removal rate of Cr（Ⅲ）was higher when the pH value of the system was adjusted after FeCl₃was added.The removal rate of Cr（Ⅲ）could reach 99.55%when the initial concentration of FeCl₃was 60mg/L.When the pH value was 3.0,the highest removal rate of total chromium removed by DTMPAM alone was 63.27%at 330 mg/L of DTMPAM dosage.However,after DTMPAM compounded with FeCl₃,the removal rate of Cr（Ⅵ）and total chromium could reach 98.64%and 90.60%,respectively.The mechanism in the process of removal of Cr（Ⅵ）and total chromium by DTMPAM alone or DTMPAM compounded with FeCl₃was the same,and FeCl₃played an important role in electrical neutralization as flocculation mechanism.（4）DTMPAM has a high removal efficiency on total Mn in water samples.When the initial concentration of Mn（Ⅶ）was 25 mg/L and the pH value of the water sample was 5.0,the optimal hydraulic conditions were set as fast stirring speed of 180 r/min,fast stirring time of 1.5 min,slow stirring speed of 50 r/min,slow stirring time of 20 min.Under the hydraulic conditions,the removal rate of total Mn could reach 100%at 135 mg/L of the DTMPAM dosage.At different initial concentrations of Mn（Ⅶ）,DTMPAM performs better in removal of Mn.（5）When the dosage of DTMPAM was low,the turbidizing substance had a promoting effect on the removal of total Mn by DTMPAM;however,when the dosage of DTMPAM was increased,the turbidity substance had a smaller inhibitory effect on the removal of total Mn by DTMPAM.DTMPAM could remove turbidity with efficiency Inorganic ions,such as K⁺,Na⁺,Ca²⁺,Mg²⁺,SO₄^2-,NO₃^-,Cl^-,had different effects on the removal of total Mn under different DTMPAM dosages.Infrared spectroscopy and energy spectrum analysis indicated that the dithiocarboxyl group on the DTMPAM molecular chain could reduce Mn（Ⅶ）to Mn（Ⅱ）in the water samples,and Mn（Ⅱ）could be further chelated with the dithiocarboxyl group and amine group on the DTMPAM molecular chain to form flocs.