Development Of Efficient And Environmentally Friendly Deicing Salt

In most countries over the world as well as in China, snowing causes terrible inconvenience to people's everyday life and big economical loss. This made snow-melting agent emerge naturally to solve such problems.The traditional snow-melting agent (eg. sodium chloride) is likely to erode metal and concrete and bring environmental damages, and then non-chloride snow-melting agent is with high price but low snow-melting property.Under the analysis of chloride-oriented and non-chloride snow-melting agents, and with the guidance of freezing point decrease theory, metal antisepsis theory, and plant damage mechanism, in this research we took chlorides as a breakthrough, checked and discovered various chlorides mixed together could be more efficient at a lower freezing point, and took thermal effect into consideration.The main works and results are listed as follows:First of all, we worked out three formulations through simplicity barycenter design with 3 main materials for producing snow-melting agents suitable to different temperature and various situation, Here is three formulation with main raw materials: Formulation PSA1 : w(CaCl₂·2H₂O) = 70%, w(MgCl₂·6H₂O) = 20%, w(L) = 10% ; Formulation PSA2: w(CaCl₂·2H₂O) = 50%, w(MgCl₂·6H₂O) = 40%, w(L) = 10%; Formulation PSA3: w(CaCl₂·2H₂O) = 30%, w(MgCl₂·6H₂O) = 60%, w(L) = 10%;It is suitable for PSA1 to be used in airport, bridge and expressway that are seated in deeply cold temperature zone (-30°C～-35°C) with higher requirement of anti-corrosion; PSA2 fits to street, park and courtyard which are local in moderate cold temperature zone (-20°C～-25°C) with general requirement of anti-corrosion and then PSA3 adapts to general road that are seated in slight temperature zone (-10°C～-15°C) with lower requirement of anti-corrosion.The PSA-series, have broken the situation that snow-melting agent variety is single, and have avoided invalidation and waste during using them.In order to release the corrosion chloride caused to metal and concrete and increase the nourishment for plants, on the base of the corrosive solution of w(PSAl) = 3%, Using orthogonal experiment technology three times, we screened out a compound corrosion retardant of PSA-series(Write it for H). The composition of H is m(T) : m(zinc dihydrogen phosphate) : w(thiourea) = 6:1:2, and it has a better result of anti-corrosion, when c(H) = 450mg/L in PSA-serie solution. This compound corrosion retardant with low price and high anti-corrosive ratio, the content of phosphorus accords with national relevant standards of farm flooding GB 5084-92.This research mensurated the ice-melting velocity of PSA-serie snow-melting agents. we found out that PSA-series possess high ice-melting velocity at -10°C, which are about twice of that of sodium chloride, and about 3 times to Calcium Magnesium acetic acid (CMA); PSA-series are of slightly difference at -20°C, and when sodium chloride nearly loses efficiency; PSA1 still has better ice-melting ability at -30°C; At the beginning, PSA-series possess higher ice-melting velocity, which is 4～5 times of that of sodium chloride, and 10 times to CMA; Considering ice-melting velocity and the result of ice-melting ability at low temperature, PSA-series are superior to sodium chloride and CMA, CMA's ice-melting velocity is very slow at -10°C, and both of them are lost the ability of ice-melting under-15°C.This research mensurated the corrosion of snow-melting agents to metal and concrete. The results show that calcium chloride is of the most corrosion ratio to carbon steel, and its corrosion ratio is 1.5 times of that of sodium chloride; sodium chloride is of the most pitting corrosive; CMA and PSA-series added compound corrosion retardant are of a little corrosion ratio, less than 50% of that of sodium chloride, even lower than that of water. Compared with sodium chloride corrosivity of the same density, PSA1, PSA2 and PSA3 corrosion ratio to the steel of carbon is 0.91%, 1.71% and 2.82% of that of sodium chloride respectively. PSA-series almost have no corrosion to concrete.Freezing points and pH values of above-mentioned snow-melting agents have been investigated , and amount of plant subjecting to the salts has also been studied. Results showed PSA-series' freezing point is lower than -30°C, pH value is between 6～9, amount of plant to bear the salts is over 150g/m², which accordes with environmental protection standard.Through the curve of freezing point decreasing and the mathematics model of snow layer, This research probed into the main material of snow-melting agents and corrosion retardant's dosage. Results showed a certainty function relation between the dosage of main materials of PSA-series and outside temperature and the dosage of snow , while the dosage of corrosion retardant is only related with the dosage of snow .At a certainty t°C, to completely melt one square meter of h centimeter snow, it needes the gram of PSA1, PSA2 and PSA3 are m₁, m₂ and m₃. It needes the gram of corrosion retardant is m'.The expression of m₁, m₂ and m₃ are:Then the Consumption of corrosion retardant is 0.018h gram.During developing PSA-series snow-melting agent, This research reserved the advantages of traditional snow-melting agent-low price and freezing point, absorbed the strong points of CMA-nearly no damage to metal and concrete and good to plant., and enriched the categories of snow-melting agent, also realized the goal of adjust measures to local conditions. The products developed in the experiment have high value of adoption, and become one of the first-choice deicers in winte. On the whole, we realized our original goal of this research-developing a new snow-melting agent that is efficient and environment-friendly.