Both PAC and PAM are water treatment chemicals.
Polyaluminum chloride (PAC), also known as basic aluminum chloride or aluminum hydroxychloride, or polyaluminum chloride, or its hydrolysis products, causes colloids in wastewater or sludge to rapidly precipitate, facilitating the separation of large particles. The molecular formula of PAC is [AL2(OH)nCl6-n]m, where n is any integer from 1 to 5, and m is the degree of polymerization, i.e., the number of chain segments, with m not exceeding 10.
The coagulation effect of PAC is closely related to the ratio of OH to AL (the value of n), usually expressed as basicity. Basicity B = [OH]/(3[AL]) x 100%. B should be between 40-60%, and the suitable pH range is 5-9.
The hydrolysis process and mechanism of iron salt coagulants are similar to those of aluminum salts.
Polyacrylamide (PAM), commonly known as a flocculant or coagulant, is a coagulant. PAM has an average molecular weight ranging from several thousand to tens of millions. Its bond-like molecules contain numerous functional groups, and it is largely ionized in water, classifying it as a high-molecular-weight electrolyte. Based on the characteristics of its dissociable groups, it is classified into anionic, cationic, and nonionic polyacrylamide.
PAM appears as a white powder, readily soluble in water, and almost insoluble in benzene, ether, esters, acetone, and other common organic solvents. Aqueous solutions of polyacrylamide are nearly transparent viscous liquids. It is a non-hazardous, non-toxic, and non-corrosive substance. Solid PAM is hygroscopic, with hygroscopicity increasing with increasing ionicity. PAM has good thermal stability; it is stable up to 100℃, but decomposes above 150℃, producing nitrogen gas and undergoing imidization between molecules, making it insoluble in water. Its density is 1.302 mg/L (23℃). Its glass transition temperature is 153℃. PAM exhibits non-Newtonian flowability under stress.
Cationic and anionic PAM are suitable for wastewater or sludge carrying negative and positive charges, respectively. Activated sludge produced by biological methods carries a negative charge, so cationic PAM should be used. Anionic PAM is effective for treating positively charged wastewater or sludge, such as wastewater from steel mills, electroplating plants, metallurgy, coal washing, and dust removal. Nonionic PAM is effective for both cationic and anionic sludge, but it is very expensive, increasing treatment costs.
