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Chemical Stabilization <br />Chemical stabilization involves mixing a reagent with mineral wastes to <br />form an air- and water-resistant crust or layer which will effectively stop <br />dusts from blowing and inhibit water erosion. Chemical stabilization has not <br />proved as durable as soil covering or vegetation. However, chemicals can be <br />used on sites unsuited to the growth of vegetation because of harsh climatic <br />conditions or the presence of vegetable poisons in the tailings, o:- in areas <br />that lack access to a soil-covering material. Chemical stabilization is also <br />applicable for erosion control on active tailings ponds. Chemicals can be <br />effectively used on portions of these ponds to restrict-air pollution while <br />other portions continue to be active. Complications arise, however, in achiev- <br />ing satisfactory chemical stabilization in r_hat the surfaces of tailings piles <br />seldom are homogeneous. Sections of slimes frequently alternate with sections <br />of sands. The permeability, reactivity, pH, and salt content of the surfaces <br />vary considerably. <br />Tests were conducted by the Bureau on several samples of acidic, neutral, <br />and basic mill tailings, of varying salt content, which were segregated into <br />sand, slime, and combined fractions to evaluate the effectiveness of various <br />reagents on differing surfaces. Since the amount of moisture in the tailings <br />affects the bonding characteristics of the reagents, this variable was also <br />investigated by wetting the tailings prior to adding the chemicals. <br />The coherency of the tailings surfaces after trea[ment was determined by <br />using air and water systems to simulate wind and water erosion. The water jet <br />used could be varied to obtain pressures impinging on the surface of the sam- <br />ples varying from 0 to 30 psi. Raindrops supposedly present a pressure of <br />5 psi when falling to earth, and this pressure was used as a general reference <br />point. The ability of the chemically produced crust to resist penetration at <br />timed intervals varying from 1 minute to several hours was determined to be a <br />function of the volume of the tailings displaced by the jet. The amount of <br />tailing displaced at the differing pressures tested on various portions of the <br />samples was considered equal to the amount of standard minus-35-plus-200-mesh <br />sand required to fill the hole and gave an empirical order of magnitude mea- <br />surement as to water erosion resistance. The water jet device used is shoran <br />in figure 1. <br />The resistance to air erosion was determined by placing samples with and <br />without chemical additions in a wind tunnel. The samples were placed hori- <br />zontal to the direction of the air flow to simulate pond areas, and at angles <br />up to 36 degrees to simulate dike areas. Air velocities from 0 to approxi- <br />mately 100 miles per hour were produced by a variable speed blower. The <br />weight of tailing displaced by the various wind velocities was measured to <br />determine the effectiveness of the various crusts in resisting wind erosion. <br />Figure 2 illustrates the wind tunnel used. <br />Seventy chemicals including lime, pyrite, sodium silicates with various <br />ratios of Si0 .•Na 0, silicates with FeSO4 and CaCl2 additives, various ligno- <br />sulfonates, redwood bark extracts, amines, acel'ate salts of amines, dicalcium <br />silicate, bituminous base products, resinous adhesives, and elastomeric <br />