Application Of Minerals And Slag To Phosphor Removal From Waste Waters: A Mechanism Study

Nourishment-enrichment in waters can produce pollution, which may account for 40 % and 65% of pollution in lakes and reservoirs in the world and in China, respectively. Phosphor is the major control over nourishment-enrichment in waters, and the main recovery approaches include engineering processes, physicochemical and biological methodology, etc. These methodologies can remove phosphor from waters;but the phosphor concentration is still above the base line for nourishment-enrichment explosion (0.01-0.02 mg/l).With reference to principles of crystal growth and mineralogy, the author conducted phosphor- removing experiment on waste waters by utilization of vermiculite, apatite and slag. The results suggest that these materials can remove phosphor from waters, among which slag and phosphor are most effective phosphor-removing agent that can reduce phosphor to the level below the critical limit for nourishment-enrichment.Slag: experiments were carried out for sewage with different concentrations from campus, at both large and small scales and at different temperatures and pH values. The results suggest that these agents are effective in phosphor-removal, and at certain circumstances phosphor concentration could be reduced to the level below the nourishment critical line. The negative side is that the outlet water has higher pH.Vermiculite: expanded vermiculite has prominent effect in phosphor-removal, which can bring nourishment in waters to the baseline of nourishment in waters. The resultant fluids, however, still has high pH value, and the P-removal effectiveness is not stable.Calcite: initial phosphor concentration and temperature are controls over the phosphor-removing effectiveness of calcite. When phosphor concentration is above 3 mg/1, and the solution is Ca- and F-bearing, and heated, phosphor concentration could be decreased to 0.026 mg/1, close to the nourishment baseline in waters. This methodology, however, is not significantly effective for sewage with P concentration lower than 1mg/l.Apatite: Input of Ca and F can efficiently remove phosphor from waters, especially for low P waters (e.g., 1 ppm and 0.5 ppm) that is close to the baseline of nourishment-rich waters. When heated or with pH=10, apatite can reduce P to the level below the critical line, which is the lowest level can be reached in P-removal from waste waters. There is no significant pH value change after P removal.Infra-spectrometer, Larman-spectrometer, SEM and TEM analysis of the precipitation suggests that the precipitation is similar to apatite in composition, with low crystallization level. Apatite works as the seed for crystal growth, while calcite does not have such a role. Therefore, the optimistic condition for P removal requires high pH, presence of Ca and F cations and apatite particles, which can reduce P concentration to the level below the baseline. The above mechanism is a Ca-P precipitation process, not an adsorption of P.