Understanding memory use in R: "cannot allocate vector of size"

Question

I have read about other people's problems with memory use, but none of them help with the following issue. I have a 64 bit R environment with 16GB of RAM.

Import .gz file of size 229MB. (the unzipped version is 921MB)

accepted_def <- read.csv(gzfile('accepted_2007_to_2017.csv.gz'), 
na.strings='')
acc_dt <- as.data.table(accepted_def)

By this time, my R Studio R session memory use has gone from about 100MB to 3GB

Clean up data and get rid of unnecessary features:

library(dplyr)
df.train <- select(acc_dt, 
-1,-2,-10,-11,-16,-19,-21,-22,-23,-26,-46,-48,-49)

Finally, attempt to impute missing values with MICE:

library(mice)
df.new = as.data.frame(mice(df.train, m=1, method = 'cart', printFlag=F))

Now, my R session memory use jumps to over 12GB and I get the following:

Error: cannot allocate vector of size 11.6 Mb

Any ideas on what is going on would be appreciated!