the present invention involves the treatment of solid waste to reduce its permeability by the addition and mixing with a treatment additive chosen by considering ( 1 ) the chemical and physical regulatory criteria ; ( 2 ) the soil and groundwater chemistry of the disposal site ; and ( 3 ) the physical characteristics of the waste itself , i . e . particle size distribution , organic content and clay content . monocalcium phosphate , which is also commonly available in a fertilizer grade as triple super phosphate or tsp , may be used alone or with portland cement to treat the waste . if the waste material is a soil , does not contain much organic matter and has an adequate amount of clay , then monocalcium phosphate additive alone may prove adequate to meet the chemical and physical criteria . this additive would provide some fines to the system , i . e . particles which would pass a # 200 sieve , and the phosphoric acid buffer system that provides stability to the treated waste mixture under minor environmental changes . if the physical criteria , i . e . permeability and unconfined compressive strength , cannot be met with the phosphate additive alone , then portland cement can be added to provide the cementatious matrix which will increase unconfined compressive strength and decrease permeability . the phosphate buffer system provided by the monocalcium phosphate additive will stabilize the system up to a certain point of portland cement addition so that it will not offset the chemical equilibrium ( portland cement shifts the ph to the high end ) and return the lead to a more soluble form . a buffer solution is one consisting of a weak acid and its conjugate base which resists ph changes when diluted or when various amounts of acid or base are added . since orthophosphoric acid ( hereinafter referred to as phosphoric acid ), the root compound of the above - listed additives , is a polyprotic acid , it disassociates or ionizes in three steps involving the following - proton - transfer equilibria : h . sub . 3 po . sub . 4 + h . sub . 2 o -. sub .-- h . sub . 2 po . sup .-. sub . 4 + h . sub . 3 o . sup .+ k . sub . 1 = 7 . 5 × 10 . sup .- 3 pk . sub . 1 = 2 . 1 ( 1 ) h . sub . 2 po . sub . 4 . sup .- + h . sub . 2 o -. sub .-- hpo . sub . 4 . sup . 2 - + h . sub . 3 o . sup .+ k . sub . 2 = 6 . 3 × 10 . sup .- 8 pk . sub . 2 = 7 . 2 ( 2 ) hpo . sub . 4 . sup . 2 - + h . sub . 2 o -. sub .-- po . sub . 4 . sup . 3 - + h . sub . 3 o . sup .+ k . sub . 3 = 4 . 8 × 10 . sup .- 13 pk . sub . 3 = 12 . 3 ( 3 ) in each of these ionization steps , the substance on the left side of the reaction arrow is the weak acid and the substance on the right is the conjugate base . therefore , three separate buffer systems are available by the addition of phosphoric acid or of its derivative salts in an aqueous solution . the chemical equilibria shifts with ph and the addition of other chemical species . in a pure phosphoric acid solution , however , at a ph of 4 . 6 , the h 2 po 4 - species totally dominates . at a ph of 7 . 2 , the equilibrium shifts to 1 / 2 h 2 po 4 - and 1 / 2 hpo 4 2 - and at a ph of 9 . 8 , the species h 2 po 4 - dominates . the maximum buffer capacity exists at the ph where equal concentrations of each species exists , or the pk value is 2 . 1 for reaction ( 1 ), 7 . 2 for reaction ( 2 ) and 12 . 3 for reaction ( 3 ). lead is known to be soluble at lower and higher ph ranges , therefore , theoretically the optimum ph of a phosphoric acid solution with lead would be 7 . 2 . the chemical equilibria of such a system , however , is subject to many additional factors ; therefore , the optimum final ph shifts with every mixture . table 1 shows the compilation of permeability data obtained in a treatability study using samples of solid waste obtained from a waste site . table 1 shows the successful treatment , by reducing the solid waste permeability , of lead contaminated solid waste by the addition of tsp either alone or in combination with the additive portland cement added for soil stability . the portland cement used is preferably as specified by astm c150 . in determining the soil physical and chemical characteristics and the proper additive for treatment of the solid waste , samples of the solid waste are used to perform the laboratory treatment tests . for example , in practicing the invention , the mix of the solid waste with the ph buffering agents must be sufficiently complete so that a random small sample , e . g . 100 grams of the waste mixture , will have sufficient agents to limit lead extraction to below 5 . 0 mg / l when the waste mixture is analyzed using the tclp . a compacted 3 - inch diameter by 6 &# 34 ; high cylinder is used to test whether sufficient agents have been added to limit the permeability to below 1 × 10 - 6 cm / s when the waste mixture is analyzed using astm d 5084 specifications . in addition , the american nuclear society ( ans ) method 16 . 1 test has been modified for use in testing the leaching characteristics of solidified waste . the modified ans 16 . 1 has been used in this application to ensure that the waste has an effective diffusivity of ≦ 1 × 10 - 12 cm 2 / s . for a specific solid waste , the appropriate ratio of agents to solid waste may be arrived at by experimentation with the above noted amount of sample of the waste having various percentages of the agents by weight . in general the percentage by weight of the additive can range from 1 % to 10 % and the percentage by weight of the portland cement can range from 3 % to 30 %. table i______________________________________sample id permeability ( cm / sec ) ______________________________________pp14 - 4a 1 . 7 × 10 . sup .- 8pp14 - 4b 1 . 0 × 10 . sup .- 8pp14 - 4c 1 . 0 × 10 . sup .- 8pp14 - 5a 3 . 1 × 10 . sup .- 8pp14 - 5b 9 . 1 × 10 . sup .- 7pp14 - 5c 3 . 7 × 10 . sup .- 8pp15 - 4a 6 . 2 × 10 . sup .- 9pp15 - 4b 2 . 5 × 10 . sup .- 8pp15 - 4c 7 . 9 × 10 . sup .- 9pp15 - 5a 8 . 3 × 10 . sup .- 9pp15 - 5b 3 . 7 × 10 . sup .- 8pp15 - 5c 6 . 9 × 10 . sup .- 94a 1 . 1 × 10 . sup .- 75a 2 . 6 × 10 . sup .- 96a 5 . 2 × 10 . sup .- 97a 6 . 0 × 10 . sup .- 99a 1 . 2 × 10 . sup .- 8______________________________________ the data in table 1 discloses that acceptable permeability coefficients were obtained , when tested in accordance with astm d 5084 specifications , when the solid waste is mixed with tsp alone or with tsp and portland cement . each sample of solid waste was prepared for testing by drying and weighing the sample , by adding between 3 . 0 and 5 . 0 percent by dry weight of tsp to each sample , by adding between 12 . 0 and 15 . 0 percent by dry weight of portland cement to some of the samples , and by curing each of the samples in 100 % humidity for at least seven days . the treatability ratios of table 1 disclose that agents of phosphoric acid such as tsp either alone or in combination with portland cement can be used to reduce permeability of solid waste below state imposed maximum criteria . it is understood that the invention is not confined to the particular process disclosed herein ; nor to the materials and substances described , but embraces such modified forms thereof as come within the scope of the following claims .
this invention relates to the treatment of contaminated materials including soils and solids to reduce its permeability , and in particular to chemical treatment of waste or solids containing high levels of heavy metals such as lead , by treating the waste or solid with an additive such as monocalcium phosphate either alone or in combination with portland cement .