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ti <br /> I <br /> 3 <br /> Chemical StabilizationI <br /> Chemical stabilization involves mixing a reagent with mineral wastes to i4i <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 !i.41 <br /> : '1' <br /> other portions continue to be active. Complications arise, however, in achiev- <br /> ing satisfactory chemical stabilization in that 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 iy�ll <br /> vary considerably. <br /> Tests were conducted by the Bureau on several samples of acidic , neutral, • �'s + <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 ;I <br /> affects the bonding characteristics of the reagents, this variable was also <br /> investigated by wetting the tailings prior to adding the chemicals. ! <br /> �I <br /> The coherency of the tailings surfaces after treatment was determined by <br /> using air and water systems to simulate wind and water erosion. The water jet IY -I <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 shown <br /> t 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 SiO .•Na 0, silicates with Fe&04 and CaC12 additives, various ligno- <br /> �; sulfonates, redwood bark extracts , amines, acetate salts of amines , dicalcium <br /> Silicate, bituminous base products , resinous adhesives, and elastomeric <br />