The commonly used activation gases are carbon dioxide, water vapor, oxygen, etc., due to the oxidation reaction of these gases on the surface of the carbonized substance, eroding the carbonized substance, thus producing a rich porous structure.(2) Chemical method.
Chemical activation method is a method of preparing activated carbon by adding chemicals to the raw materials used or impregnation into the raw materials or carbonized materials, and then heating it at high temperature in inert gas.The chemicals used in chemical activation are generally dehydrating.The more commonly used activator is: inorganic acid varieties have phosphoric acid, sulfuric acid and boric acid, salt varieties have zinc chloride, calcium carbonate and potassium sulfate, alkali varieties have sodium hydroxide, potassium hydroxide, etc.
The main principle of chemical activation method is the raw materials in 0.5~5 times the chemical activator impregnation for a certain time, in the process of heating, because of the dehydration of chemicals, the H and О elements in the raw materials in the form of water vapor released, the results produced a developed porous structure of activated carbon.The method requires the oxygen content in the raw material.25%, hydrogen content ≥5%[4], and most of the materials that can meet the requirements of this index are rice husk, wood and coal, etcwhich conforms to the scientific concept of circular economy and sustainable development.
In this paper, the sludge of the municipal sewage plant was used as raw material, and the activated carbon was prepared by chemical activation method, and the adsorption of lead and cadmium was studied with it, so as to realize the use of waste for waste control. The conclusions are as follows:(1) According to the relevant national standards, the sludge of Liede Sewage Treatment Plant is mainly composed of volatile organic compounds, with a volatile content of 64.86%, which can be used as the main raw material for the preparation of activated carbon.
(2) Without adding additives to the sludge, the concentration of sulfuric acid and zinc chloride is 4 mol·L' and the volume ratio is 2:1. The activated carbon prepared has the maximum iodine adsorption value of 549.6 mg·g 'and the yield of 51.3%, which is the better carbon sample prepared by pure sludge and is recorded as SAC.(3) Adding 8% peanut shell, the iodine value of activated carbon of sludge reached 789.6mg · g', which was recorded as PAC;
By single factor experiment, the optimal conditions of carbon production were obtained as follows: pyrolysis temperature 600℃, activator concentration 4 mol · L', pyrolysis time 1.5h, solid-liquid ratio 1:2.5.Orthogonal experiment showed that the influence of each factor was as follows: pyrolysis temperatureIs the activator concentration Pyrolysis time >Solid-liquid ratio.(4) the main performance of PAC is basically equivalent to 8818 type activated carbon;
The concentrations of heavy metals in activated carbon leaching solution of sludge were all qualified.Compared with domestic and foreign research reports, the quality of PAC is in the middle level.(5) Compared with SAC, the specific surface area of PAC is larger, up to 636.8m2·g'. PAC is mainly mesoporous, but also contains some micropores. The adsorption/desorption isotherm shows that PAC is activated carbon with parallel wall slit pore structure.